Search

The purpose of this study was to investigate whether 6 weeks of static hamstring stretching effects range of motion (ROM), sprint, and vertical jump performances in athletes. Twenty-one healthy division III women's track and field athletes participated in the study. Subjects were tested for bilateral knee ROM; 55-m sprint time; and vertical jump height before, at 3 weeks, and after the 6-week flexibility program. Subjects were randomly assigned to treatment and control groups and warmed up with a 10-minute jog on a track before a hamstring stretching protocol. The stretching protocol consisted of four repetitions held for 45 seconds, 4 days per week. Four variables (left and right leg ROM, 55-m sprint time, vertical jump) were analyzed using a repeated-measures analysis of variance design. No significant differences (P < or = 0.05) were found with any of the four variables between the stretching and control groups. Six weeks of a static hamstring stretching protocol did not improve knee ROM or sprint and vertical jump performances in women track and field athletes. The use of static stretching should be restricted to post practice or competition because of the detrimental effects reported throughout the literature. Based on the current investigation, it does not seem that chronic static stretching has a positive or negative impact on athletic performance. Thus, the efficacy of utilizing this practice is questionable and requires further investigation. [ABSTRACT FROM AUTHOR]

Context: Adults perceive certain factors to increase or decrease the risk of sustaining running-related injuries, but many of their perceptions are not supported by research. Little is known about the perceptions that adolescent runners hold. Investigating perceptions for adolescent runners is needed to assist in the development of future injury educational materials, as these resources may need to be tailored differently for adolescents and adults., Objective: To identify factors that adolescent runners perceive as risk or protective factors for running-related injuries and to compare these perceptions with those of adult runners., Design: Cross-sectional study., Setting: Online survey., Patients or Other Participants: We surveyed 302 adolescent (164 females, 138 males; age = 16.0 ± 1.4 years [range, 12-19 years]) and 357 adult runners (197 women, 160 men; age = 40.7 ± 11.8 years [range, 20-77 years])., Main Outcome Measure(s): Participants completed a survey with questions about whether factors related to training habits, footwear, biomechanics, strength, stretching, or nutrition influence the risk of sustaining a running-related injury. If ≥75% of adolescents indicated that a factor increases or decreases the risk of sustaining an injury, we considered that factor to be a perceived risk or protective factor, respectively. We also performed Fisher's exact test to compare the proportion of adolescent and adult runners who responded with "increase," "decrease," "neither increase or decrease," or "I don't know" to each question., Results: Adolescent runners perceived training habits, footwear, biomechanics, strength, stretching, and nutrition to increase or decrease the risk of sustaining a running-related injury. A larger proportion of adolescents than adults perceived that more footwear cushioning and stretching decrease injury risk, but a smaller proportion perceived that overtraining increases injury risk and strength decreases injury risk., Conclusions: Differences in perceptions exist between adolescent and adult runners, and future educational materials and research questions may need to be tailored for different running populations., (© by the National Athletic Trainers’ Association, Inc.)

Objectives: To investigate the intra-rater reliability and validity of belt-stabilized and tension dynamometry to assess hip muscle strength and power., Design: Repeated measures., Setting: Biomechanics laboratory., Participants: Seventeen uninjured adults (age = 22.0 ± 2.3y; 13 females)., Main Outcomes Measures: Peak torque (strength) and rate of torque development (RTD; power) were measured for hip abduction, internal rotation, external rotation and extension using an isokinetic dynamometer, and belt-stabilized and tension dynamometry., Results: For peak torque assessment, belt-stabilized and tension dynamometry showed good (Intraclass Correlation Coefficient [ICC] = 0.848-0.899) and good-to-excellent (ICC = 0.848-0.942) reliability, respectively. For RTD, belt-stabilized dynamometry showed fair reliability for abduction (ICC = 0.524) and good reliability for hip internal rotation, external rotation, and extension (ICC = 0.702-0.899). Tension dynamometry showed good reliability for all motions when measuring RTD (ICC = 0.737-0.897). Compared to isokinetic dynamometry, belt-stabilized and tension dynamometry showed good-to-excellent correlations for peak torque assessment (r = 0.503-0.870), and fair-to-good correlations for RTD (r = 0.438-0.674). Bland-Altman analysis showed that measures from belt-stabilized and tension dynamometry had clinically meaningful disagreement with isokinetic dynamometry., Conclusion: Tension dynamometry is reliable for assessing hip strength and power in all assessed motions. Belt-stabilized dynamometry is reliable for assessing internal rotation, external rotation, and extension. Validity of both methods is questionable, considering the lack of agreement with isokinetic dynamometry., Competing Interests: Declaration of competing interest None declared., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Context: High secondary injury rates after orthopedic surgeries have motivated concern toward the construct validity of return-to-sport test batteries, as it is evident that common strength and functional assessments fail to elicit pertinent behaviors like visual search and reactive decision making. This study aimed to establish the test-retest reliability of 2 reactive agility tasks and evaluate the impact of visual perturbation on physical performance., Methods: Fourteen physically active individuals completed 2 agility tasks with reaction time (ie, 4 corner agility), working memory, and pathfinding (ie, color recall) components. Participants completed both tasks 4 times in 2 sessions scheduled 7 days apart. Outcomes included performance metrics of reaction time, time to target, number of targets, and total time assessed with reactive training timing gates. To assess test-retest reliability, we used intraclass correlation coefficients (ICCs), standard error of measurement (SEM), and minimal detectable change (MDC). Stroboscopic goggles induced visual perturbation during the fourth trial of each task. To assess the effect of visual perturbation, we used paired t tests and calculated performance costs., Results: The 4-corner agility task demonstrated excellent reliability with respect to reaction time (ICC3,1 = .907, SEM = 0.13, MDC = 0.35 s); time to light (ICC3,1 = .935, SEM = 0.07, MDC = 0.18 s); and number of lights (ICC3,1 = .800, SEM = 0.24, MDC = 0.66 lights). The color recall task demonstrated good-to-excellent test-retest reliability for time to lights (ICC3,1 = .818-.953, SEM = 0.07-0.27, MDC = 0.19-0.74 s); test time (ICC3,1 = .969, SEM = 5.43, MDC = 15.04 s); and errors (ICC3,1 = .882, SEM = 0.19, MDC = 0.53 errors). Visual perturbation resulted in increased time to target (P = .022-.011), number of targets (P = .039), and total test time (P = .013) representing moderate magnitude degradation of performance (d = 0.55-0.87, performance costs = 5%-12%)., Conclusions: Both tasks demonstrated acceptable test-retest reliability. Performance degraded on both tasks with the presence of visual perturbation. These results suggest standardized reactive agility tasks are reliable and could be developed as components of dynamic RTS testing.

Background: Impairments in hamstring strength, flexibility, and morphology have been associated with altered knee biomechanics, pain, and function. Determining the presence of these impairments in individuals with gradual-onset knee disorders is important and may indicate targets for assessment and rehabilitation. This systematic review aimed to synthesize the literature to determine the presence of impairments in hamstring strength, flexibility, and morphology in individuals with gradual-onset knee disorders., Methods: Five databases (MEDLINE, Embase, CINAHL, SPORTDiscus, and Web of Science) were searched from inception to September 2022. Only studies comparing hamstring outcomes (e.g., strength, flexibility, and/or morphology) between individuals with gradual-onset knee disorders and their unaffected limbs or pain-free controls were included. Meta-analyses for each knee disorder were performed. Outcome-level certainty was assessed using the Grading of Recommendations Assessment, Development, and Evaluation, and evidence gap maps were created., Results: Seventy-nine studies across 4 different gradual-onset knee disorders (i.e., knee osteoarthritis (OA), patellofemoral pain (PFP), chondromalacia patellae, and patellar tendinopathy) were included. Individuals with knee OA presented with reduced hamstring strength compared to pain-free controls during isometric (standard mean difference (SMD) = -0.76, 95% confidence interval (95%CI) : -1.32 to -0.21) and concentric contractions (SMD = -0.97, 95%CI : -1.49 to -0.45). Individuals with PFP presented with reduced hamstring strength compared to pain-free controls during isometric (SMD = -0.48, 95%CI : -0.82 to -0.14), concentric (SMD = -1.07, 95%CI : -2.08 to -0.06), and eccentric contractions (SMD = -0.59, 95%CI : -0.97 to -0.21). No differences were observed in individuals with patellar tendinopathy. Individuals with PFP presented with reduced hamstring flexibility when compared to pain-free controls (SMD = -0.76, 95%CI : -1.15 to -0.36). Evidence gap maps identified insufficient evidence for chondromalacia patellae and hamstring morphology across all gradual-onset knee disorders., Conclusion: Our findings suggest that assessing and targeting impairments in hamstring strength and flexibility during rehabilitation may be recommended for individuals with knee OA or PFP., (Copyright © 2023. Production and hosting by Elsevier B.V.)

Background/purpose: Return to sport decision-making may be improved by assessing an athlete's ability to coordinate movement with opponents in sport. The purpose was to investigate whether previous injuries associated with female soccer players' interpersonal coordination during a collision avoidance task. The authors hypothesized that external perturbations would disrupt the strength and stability of coordinated movement, and that individuals with a history of injury would be less likely to recover coordinated movement., Study Design: Cross-Sectional., Methods: Nine female athletes with a history of lower extremity injuries and nine without injuries were paired into dyads. Each dyad completed twenty trials of an externally paced collision-avoidance agility task with an unanticipated perturbation. Participant trajectories were digitized and analyzed using cross-recurrence quantification analysis (CRQA) to determine the strength and stability of interpersonal coordination dynamics. Trials in which participants with injury history assumed leader or follower roles within each dyad were then used to study how dyadic coordination varied across task stages (early, perturbation, and late) using linear mixed effect models. Cohen's d effect sizes were calculated to demonstrate magnitude of differences. In exploratory analysis, psychological readiness (i.e., self-reported knee functioning, fear of injury, and risk-taking propensity) was evaluated for their association with leader-follower status., Results: Perturbation disrupted the strength (R2=0.65, p<0.001, early=49.7±1.7, perturbation=41.1±1.7, d=0.39) and stability (R2=0.71, p < 0.001, early=65.0±1.6, perturbation=58.0±1.7, d=0.38) of interpersonal coordination regardless of leader-follower status. Individuals with injury history failed to restore coordination after the perturbation compared to control participants (injury=44.2.0±2.1, control=50.8±2.6, d=0.39). Neither demographic nor psychological measures were associated with leader-follower roles (B=0.039, p=0.224)., Conclusion: Individuals with a history of lower extremity injury may have a diminished ability to adapt interpersonal coordination to perturbations, possibly contributing to a higher risk of re-injury., Level of Evidence: 3., Competing Interests: The authors report no competing interests., (© The Author(s).)

Introduction: Adolescent athletes involved in sports that involve cutting and landing maneuvers have an increased risk of anterior cruciate ligament (ACL) tears, highlighting the importance of identifying risky movement patterns such as dynamic knee valgus (DKV). Qualitative movement screenings have explored two-dimensional (2D) scoring criteria for DKV, however, there remains limited data on the validity of these screening tools. Determining a 2D scoring criterion for DKV that closely aligns with three-dimensional (3D) biomechanical measures will allow for the identification of poor knee position in adolescent athletes on a broad scale. The purpose of this study was to establish a 2D scoring criterion that corresponds to 3D biomechanical measures of DKV., Methods: A total of 41 adolescent female club volleyball athletes performed a three-task movement screen consisting of a single-leg squat (SLS), single-leg drop landing (SLDL), and double-leg vertical jump (DLVJ). A single rater scored 2D videos of each task using four criteria for poor knee position. A motion capture system was used to calculate 3D joint angles, including pelvic obliquity, hip adduction, knee abduction, ankle eversion, and foot progression angle. Receiver operating characteristic curves were created for each 2D scoring criterion to determine cut points for the presence of movement faults, and areas under the curve (AUC) were computed to describe the accuracy of each 2D criterion compared to 3D biomechanical data., Results: 3D measures indicated knee abduction angles between 2.4°-4.6° (SD 4.1°-4.3°) at the time point when the center of the knee joint was most medial during the three tasks. AUCs were between 0.62 and 0.93 across scoring items. The MEDIAL scoring item, defined as the knee joint positioned inside the medial border of the shoe, demonstrated the greatest association to components of DKV, with AUCs ranging from 0.67 to 0.93., Conclusion: The MEDIAL scoring criterion demonstrated the best performance in distinguishing components of DKV, specifically pelvic obliquity, hip adduction, ankle eversion, and foot progression. Along with the previously published scoring definitions for trunk-specific risk factors, the authors suggest that the MEDIAL criterion may be the most indicative of DKV, given an association with 3D biomechanical risk factors., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2024 Erdman, Loewen, Dressing, Wyatt, Oliver, Butler, Sugimoto, Black, Tulchin-Francis, Bazett-Jones, Janosky and Ulman.)

Context: People with patellofemoral pain (PFP) may have lower performance during the forward step-down and single-leg hop with their painful (unilateral complaints) or most painful (bilateral complaints) limb when compared to pain-free controls. Yet, no study has investigated the appropriateness of using the pain-free/less painful limb as a reference standard in clinical practice or whether deficits might be present depending on the laterality of pain., Objective: To compare performance scores and proportion of side-to-side limb symmetry during the forward step-down and single-leg hop tests among people with unilateral and bilateral PFP, and pain-free controls., Design: Cross-sectional study., Setting: Laboratory., Patients or Other Participants: Fifty-two young adults (18-35 years old) with unilateral PFP, 72 with bilateral PFP, and 76 controls., Main Outcome Measure(s): Group-by-limb interactions on the performance during the step- down (repetitions) and hop test (distance [cm] normalized by the limb length) were investigated using a repeated-measures analysis of covariance controlling for sex. Pairwise comparisons were interpreted using effect sizes. A Chi-square test was used to compare the proportion of symmetry/asymmetry (cutoff point of ≥ 90% for symmetries indices) across groups and tests., Results: Main effects for groups (small-to-medium effects) but not limbs indicated lower performance of both limbs of individuals with unilateral and bilateral PFP compared to controls during forward step-downs and single-leg hop tests. No significant differences for the proportion of symmetry/asymmetry were identified across groups (p ≥ 0.05), which further suggests an impaired physical performance of the contralateral limb., Conclusions: Our results indicate bilateral deficits in the physical performance of people with unilateral and bilateral PFP when compared to pain-free controls during the forward step-down and single-leg hop tests. Limb symmetries indices greater than 90% should be interpreted with caution, as they may overstate the physical performance by not assuming bilateral deficits., Competing Interests: Conflicts Of Interest: We affirm that we have no other conflicts of interest (e.g., personal associations or involvement) that have played a role in the design, execution, analysis and interpretation of data or writing of this manuscript.

Background: Patellofemoral pain (PFP) is a prevalent musculoskeletal disorder associated with functional impairments. Although postural control is commonly assessed in people with PFP, there are inconsistent results regarding potential postural control deficits in this population., Research Question: This review aims to evaluate whether postural control is impaired in people with patellofemoral pain (PFP) and the effectiveness of interventions on postural control measures., Methods: We searched six databases from their inception to May 5, 2023. We included studies assessing clinic- or laboratory-based postural control measures in people with PFP compared to pain-free controls, and intervention studies with PFP populations. We assessed risk of bias using the Joanna Briggs Institute critical appraisal checklists and the Cochrane Risk of Bias 2 tool. We assessed the certainty of evidence using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. We used random-effects meta-analyses considering subgroups based on type of task, measure, and intervention., Results: Fifty-three studies were included. Very low certainty evidence indicated that people with PFP have shorter anterior (SMD = 0.53, 95 %CI:0.16,0.90), posteromedial (SMD = 0.54, 95 %CI:0.04,1.03) and posterolateral (SMD = 0.59, 95 %CI:0.11,1.07) reach distance, and worse composite score (SMD = 0.46, 95 %CI:0.22,0.70). Very low to moderate certainty evidence indicated that people with PFP have worse anterior-posterior and overall stability indexes during single-leg stance (SMD = -0.71, 95 %CI:-1.29,-0.14; SMD = -0.63, 95 %CI:-0.94,-0.32) and overall stability index during double-leg stance (SMD = -0.39, 95 %CI:-0.78,-0.00), but no differences in center of pressure area during stair ascent (SMD = 0.32, 95 %CI:-2.72, 3.36). Low certainty evidence indicated that kinesio taping improved anterior reach distance (SMD = -0.49, 95 %CI:-0.89,-0.09), while no significant differences were observed between pre- and post-intervention outcomes for conventional rehabilitation and rigid taping., Significance: Clinicians should use clinic- (star excursion or Y-balance tests) and laboratory-based (stability indexes) measures to identify impairments of postural control in people with PFP. Low certainty of evidence suggests short-term improvement in postural control with kinesio taping., Competing Interests: Declaration of Competing Interest We affirm that we have no financial affiliation or involvement with any commercial organization that has a direct financial interest in any matter included in this manuscript. We also affirm that we have no other conflict of interest (e.g., personal associations or involvement) that has played a role in the design, execution, analysis and interpretation of data or writing of this manuscript. Each of the authors has read and concurs with the content in the final manuscript. The material within has not been and will not be submitted for publication elsewhere except as an abstract., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Adolescents undergo a period of motor incoordination during puberty characterized by high movement variability. It is unknown if differences in running kinematics variability exist among adolescent long-distance runners., Research Question: Is kinematic variability different among male and female adolescent long-distance runners of different stages of physical maturation?, Methods: We enrolled 114 adolescent long-distance runners (ages 8-19, F = 55, M = 59) in this secondary analysis of a larger cross-sectional study. Participants completed a three-dimensional overground running analysis at a comfortable self-selected speed. Peak frontal, sagittal, and transverse plane hip, knee, and ankle/shoe joint angles from the right leg were identified during stance phase for at least five trials. Variability in running kinematics was quantified as the standard deviation of the peak joint angles among the running trials for each participant. Participants were stratified by sex and stage of physical maturation (pre-, mid-, post-pubertal) and two-way ANOVAs compared between-subjects variability among groups (p ≤ .05)., Results: Significant sex by maturation interactions were observed for hip external rotation and ankle external rotation variability. Sex differences were observed for hip internal rotation, with males demonstrating greater variability, and ankle internal rotation, with females demonstrating greater variability. Pre-pubertal runners demonstrated significantly greater variability than mid-pubertal runners for hip flexion, and greater variability than post-pubertal runners for hip flexion, hip adduction, hip internal rotation, and knee flexion., Significance: Pre-pubertal adolescent long-distance runners demonstrate greater stance phase variability in running kinematics than post-pubertal adolescent long-distance runners, while adolescent males and females demonstrate similar variability. Anthropometric and neuromuscular changes that occur during puberty likely influence running patterns and may contribute to more consistent kinematic patterns for post-pubertal runners., Competing Interests: Declaration of Competing Interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome., (Copyright © 2023 Elsevier B.V. All rights reserved.)

OBJECTIVE: To summarize the evidence on reliability and criterion validity of hip muscle strength testing using portable dynamometers. DESIGN: Systematic review with meta-analysis. LITERATURE SEARCH: Five databases were searched from inception to March 2023. STUDY SELECTION CRITERIA: We included studies investigating reliability or criterion validity of hip flexor, extensor, abductor, adductor, or internal/external rotator strength testing with portable dynamometers in injury-free individuals or those with pelvic/lower limb musculoskeletal disorders. DATA SYNTHESIS: We performed meta-analyses for each muscle group, position, and method of fixation. We rated pooled results as sufficient (>75% of studies with correlations ≥0.70), insufficient (>75% of studies with correlations <0.70), or inconsistent (sufficient/insufficient results). We assessed the quality of evidence, created evidence gap maps, and made clinical recommendations. RESULTS: We included a total of 107 studies (reliability 103, validity 14). The intrarater and interrater reliability for hip muscle strength testing across different positions and methods of fixation was sufficient (intraclass correlation coefficient = 0.78-0.96) with low- to high-quality evidence. Criterion validity was less investigated and mostly inconsistent (very low-to moderate-quality evidence) with a wide range of correlations (r = 0.40-0.93). CONCLUSION: Hip muscle strength testing using portable dynamometers is reliable. The use of portable dynamometers as clinical surrogates for measuring strength using an isokinetic dynamometer requires further investigation. Clinicians testing hip muscle strength with portable dynamometers should use external fixation seated for hip flexors, prone or supine for hip extensors, side-lying or supine for abductors and adductors, and prone and seated for internal and external rotators. J Orthop Sports Phys Ther 2023;53(11):655-672. Epub 3 October 2023. doi:10.2519/jospt.2023.12045 .

Purpose: A decline in youth running was observed at the start of the COVID-19 pandemic. We investigated whether the resumption of organized running after social distancing restrictions changed running habits or injury frequency in adolescent runners., Methods: Adolescents (age = 16.1 [2.1] y) who participated in long-distance running activities completed an online survey in the Spring and Fall of 2020. Participants self-reported average weekly running habits and whether they sustained an injury during the Fall 2020 season. Poisson regression models and 1-way analysis of variance compared running habits while Fisher exact test compared differences in frequencies of injuries during Fall 2020 among season statuses (full, delayed, and canceled)., Results: All runners, regardless of season status, increased weekly distance during Fall 2020. Only runners with a full Fall 2020 season ran more times per week and more high-intensity runs per week compared with their Spring 2020 running habits. There were no differences in running volume or running-related injury frequency among Fall 2020 season statuses., Conclusions: There were no significant differences in running-related injury (RRI) frequency among runners, regardless of season status, following the resumption of cross-country. Health care providers may need to prepare for runners to increase running volume and intensity following the resumption of organized team activities.

For adults, increasing cadence reduces ground reaction forces, but a lower preferred cadence does not predispose adults to experience higher ground reaction forces. Pubertal growth and motor control changes influence running mechanics, but it is unknown if preferred cadence or step length are associated with ground reaction forces for pre-adolescent and adolescent runners. Pre-adolescent and adolescent runners underwent an overground running analysis at a self-selected speed. Mixed model multiple linear regressions investigated the associations of preferred cadence, step length, physical maturation, and sex on ground reaction forces, while accounting for running speed and leg length. Running with a lower preferred cadence or longer preferred step length was associated with larger peak braking and vertical forces ( p  ≤ .01), being less physically mature was associated with larger vertical impact peak force and vertical loading rate ( p  ≤ .01), and being a male was associated with larger loading rates ( p  ≤ .01). A lower preferred cadence or longer preferred step length were associated with higher braking and vertical forces and being less physically mature or a male were associated with higher loading rates. An intervention to increase cadence/decrease step length could be considered if ground reaction forces are a concern for an adolescent runner.

Objective: To compare brain activity between individuals with anterior cruciate ligament reconstruction (ACLR) and controls during balance. To determine the influence of neuromodulatory interventions (external focus of attention [EF] and transcutaneous electrical nerve stimulation [TENS]) on cortical activity and balance performance., Methods: Individuals with ACLR (n = 20) and controls (n = 20) performed a single-limb balance task under four conditions: internal focus (IF), object-based-EF, target-based-EF, and TENS. Electroencephalographic signals were decomposed, localized, and clustered to generate power spectral density in theta and alpha-2 frequency bands., Results: Participants with ACLR had higher motor-planning (d = 0.5), lower sensory (d = 0.6), and lower motor activity (d = 0.4-0.8), while exhibiting faster sway velocity (d = 0.4) than controls across all conditions. Target-based-EF decreased motor-planning (d = 0.1-0.4) and increased visual (d = 0.2), bilateral sensory (d = 0.3-0.4), and bilateral motor (d = 0.4-0.5) activity in both groups compared to all other conditions. Neither EF conditions nor TENS changed balance performance., Conclusions: Individuals with ACLR exhibit lower sensory and motor processing, higher motor planning demands, and greater motor inhibition compared to controls, suggesting visual-dependence and less automatic balance control. Target-based-EF resulted in favorable reductions in motor-planning and increases in somatosensory and motor activity, transient effects in line with impairments after ACLR., Significance: Sensorimotor neuroplasticity underlies balance deficits in individuals with ACLR. Neuromodulatory interventions such as focus of attention may induce favorable neuroplasticity along with performance benefits., Competing Interests: Conflict of interest statement The authors have no competing interests to declare., (Copyright © 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Purpose: This study aimed to compare quadriceps corticomuscular coherence (CMC) and force steadiness between individuals with anterior cruciate ligament reconstruction (ACLR) and uninjured controls during a force tracing task., Methods: Individuals with ACLR ( n = 20) and controls ( n = 20) performed a knee extension force-control task at 50% of maximal voluntary effort. Electrocortical activity, electromyographic activity, and torque output were recorded concurrently. CMC in beta (13-30 Hz) and gamma (31-80 Hz) frequency bands was assessed using partial directed coherence between the contralateral motor cortex (e.g., C4-C2-Cz electrodes) and the ipsilateral quadriceps muscles (e.g., left vastus medialis and lateralis). Force steadiness was quantified using root-mean-square error and coefficient of variation. Active motor threshold was determined using transcranial magnetic stimulation. Differences between groups (ACLR vs control) and limbs (involved vs uninvolved) were assessed using peak knee extension strength and active motor threshold as a priori covariates., Results: Participants with ACLR had lower gamma band connectivity bilaterally when compared with controls (vastus medialis: d = 0.8; vastus lateralis: d = 0.7). Further, the ACLR group demonstrated worse quadriceps force steadiness (root-mean-square error, d = 0.5), lower involved limb quadriceps strength ( d = 1.1), and higher active motor threshold ( d = 1.0) compared with controls., Conclusions: Lower quadriceps gamma band CMC in the ACLR group suggests lower cortical drive (e.g., corticomotor decoupling) to the quadriceps compared with matched controls. Further, the ACLR group demonstrated worse quadriceps force steadiness, suggesting impaired ability to modulate quadriceps neuromuscular control. Notably, CMC differences were present only in the gamma frequency band, suggesting impairments may be specific to multisensory integration and force modulation., (Copyright © 2022 by the American College of Sports Medicine.)

Objectives: Despite the growing use of whole-body vibration (WBV) to enhance quadriceps neuromuscular function, the hamstrings-specific response is unclear among those without neuromuscular impairment, which is important to inform performance-based recommendations. Our objective was to determine the immediate and prolonged effects of WBV on hamstrings and quadriceps neuromuscular function in uninjured individuals., Design: Crossover., Setting: Laboratory., Participants: Nineteen, recreationally active individuals performed WBV and control exercise protocols, consisting of six 1-min repetitions of isometric squats, on separate days in a randomized order., Main Outcome Measures: Electromyographic (EMG) amplitude, antagonist-to-agonist co-activation, rate of torque development, and peak torque of the hamstrings and quadriceps were measured pre-, immediately post-, and 20 min post-condition. Percentage change scores were calculated from baseline to each post-measurement., Results: A condition main effect indicated that WBV reduced agonist semitendinosus EMG amplitudes more than the control (-12.1% vs. -1.5%, p < .001). Antagonist vastus medialis EMG amplitudes were reduced immediately, but not 20 min following WBV (-7.1% vs. 3.5%, p < .001)., Conclusions: WBV induced an inhibitory effect on medial hamstrings activity during knee flexion contraction in a majority of our sample, yet this response was not uniformly observed and its functional relevance remains unclear in an uninjured population., Competing Interests: Declaration of competing interest None declared., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Purpose: The purpose of this study is to compare cortical motor planning activity during response selection and motor execution processes between individuals with anterior cruciate ligament reconstruction (ACLR) and uninjured controls during a reaction time and response selection task., Methods: Individuals with ACLR ( n = 20) and controls ( n = 20) performed a lateralized choice reaction time (e.g., Go/NoGo) task. Electrocortical activity and reaction time were recorded concurrently using electroencephalography and inertial measurement units. Separate stimulus locked and response-locked event-related potentials were computed for each limb. The lateralized readiness potential (LRP) was computed as the interhemispheric differences between waveforms and the mean LRP area and onset latency were recorded. Active motor threshold was determined using transcranial magnetic stimulation. Differences between groups (ACLR vs control) and limbs (involved vs uninvolved) and the associations between LRP characteristics and response performance (number of errors) were assessed., Results: Participants with ACLR have had smaller LRP area during periods of response selection ( P = 0.043, d = 0.4) and motor execution ( P = 0.015, d = 0.5) and committed more errors in both Go ( P < 0.001, d = 0.8) and NoGo ( P = 0.032, d = 0.5) response conditions. There were no differences in latency of response selection or motor execution. Participants with ACLR had higher active motor thresholds ( P < 0.001, d = 1.3) than controls, which was weakly associated with smaller LRP areas ( r = 0.32-0.42, P < 0.05)., Conclusions: The ACLR group demonstrated greater motor planning and response inhibition during a choice reaction time task. More errant performance also suggests poorer decision making in the presence of a "speed-accuracy" trade-off. Key features of the sample, including lower corticospinal excitability, lend support to an interpretation of widespread cortical inhibition contributing to impairments in response selection and motor execution., (Copyright © 2022 by the American College of Sports Medicine.)

Patellofemoral pain (PFP) is a chronic condition that presents with patellar pain during various daily and recreational activities. Individuals with PFP have a wide range of impairments that result in long-term disability and reduced quality of life. Current interventions target hip muscle weakness with strength-based exercises, but recurrence rates are as high as 90%. A single feasibility study demonstrated success with power-based exercises; however, there is limited evidence evaluating pain or self-reported function in larger cohorts, and no study has assessed recurrence rates. This protocol details a study evaluating a strength-based rehabilitation programme compared with a strength-based programme incorporating power-based exercises in individuals with PFP. This single-blinded randomised controlled trial will evaluate 88 participants with PFP, aged 18-40 years old. Participants will be recruited from three universities, the surrounding community and sports medicine clinics. Participants will receive three telemedicine rehabilitation sessions a week for 6 weeks. The rehabilitation programme will consist of either strength-based exercises or a combination of power and strength-based exercises. Pain, subjective function and recurrence rates will be assessed at baseline, immediately after the intervention and at four follow-up time points: 6-month, 12-month, 18-month and 24-month postintervention. We will also assess neuromuscular function of the hips and global rating of change at each postintervention time point. Trial registration number NCT05403944., Competing Interests: Competing interests: None., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY. Published by BMJ.)

Background: This is a protocol for a prospective longitudinal study that aims to investigate: (1) group-by-time changes over a minimum of 15 months follow-up in patellofemoral pain (PFP) symptoms, biomechanical, muscle function, pain processing, and psychological features; (2) the extent to which changes in biomechanical, muscle function, pain processing, and psychological features are associated with changes in self-reported pain, physical performance measures, self-reported function, health-related quality of life (HRQOL), and physical activity level., Methods: Individuals with PFP ( n  = 144) and control individuals ( n  = 85) without PFP were assessed at baseline. Outcomes assessed included: 3D kinematics and kinetics during single leg squat, step-down and single leg hop; maximal torque and rate of torque development of hip abductors and knee extensors/flexors; force steadiness of hip abductors and knee extensors; anterior and lateral trunk endurance; pressure pain thresholds at the center of patella and contralateral shoulder; kinesiophobia (Tampa Scale for Kinesiophobia); pain catastrophizing (Pain Catastrophizing Scale); worst self-reported pain (Visual Analogue Scale); physical performance measures (Single Leg Hop Test and Forward Step-Down Test); self-reported function (Anterior Knee Pain Scale); HRQOL (Medical Outcome Short-Form 36), and physical activity level (Baecke's Questionnaire). Follow-up assessments will be identical to the baseline and will be performed after a minimum of 15 months. Generalized linear mixed model (GLMM) will be used to investigate group-by-time differences. Linear regression models will be used to determine the extent to which changes in biomechanical, muscle function, pain processing, and psychological features are associated with changes in self-reported pain, physical performance measures, self-reported function, HRQOL, and physical activity level., Discussion: Physical and non-physical features have been previously associated with PFP. However, the present study will be the first to investigate their integrated evolution as part of the natural history of PFP and its progression. In doing so, we will be able to determine their behavior in the long-term, as well as how they prospectively associate with each other and with clinical outcomes. Ultimately, this will provide a greater understanding of predictors of long-term outcome and possible targets for interventions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Botta, Waiteman, Ducatti, Garcia, Farinelli, Bazett-Jones, Briani and Azevedo.)

Few studies have investigated the validity of 2D pose estimation models to evaluate kinematics throughout a motion and none have included adolescents. Adolescent athletes completed single-leg squats while 3D kinematic data and 2D sagittal and frontal plane videos were recorded. Sagittal and frontal plane joint motion throughout the single-leg squats and angles at peak knee flexion were compared among 2D pose estimation, 3D motion analysis, and traditional 2D motion analysis techniques. Statistical parametric mapping compared waveforms while Pearson's correlation compared the relationships of joint angles at peak knee flexion among techniques, respectively. We observed significant waveform differences between 2D pose estimation and 3D motion analysis at the beginning and end of the squat for sagittal plane hip and knee motion, for most of the squat for frontal plane hip motion, and throughout the entire squat for sagittal plane ankle motion and frontal plane pelvic motion. We observed moderate-to-strong relationships (r = 0.68-0.94) for sagittal plane joint angles between 2D pose estimation and 3D techniques. We observed fair correlations (r = 0.53-0.54) for frontal plane pelvic and hip joint angles between 2D pose estimation and 3D motion analysis. We observed poor relationships for the frontal plane knee angle between 3D motion analysis with 2D pose estimation (r = 0.20) and traditional 2D motion analysis (r = 0.05), respectively, but observed a strong relationship (r = 0.95) between the 2D techniques. 2D pose estimation is a valid alternative to 3D motion analysis and traditional 2D motion analysis for evaluating most sagittal and frontal plane angles during a single-leg squatting task., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: Lower cadence has been previously associated with injury in long-distance runners. Variations in cadence may be related to experience, speed, and anthropometric variables. It is unknown what factors, if any, predict cadence in healthy youth long-distance runners., Research Question: Are demographic, anthropometric and/or biomechanical variables able to predict cadence in healthy youth long-distance runners., Methods: A cohort of 138 uninjured youth long-distance runners (M = 62, F = 76; Mean ± SD; age = 13.7 ± 2.7; mass = 47.9 ± 13.6 kg; height = 157.9 ± 14.5 cm; running volume = 19.2 ± 20.6 km/wk; running experience: males = 3.5 ± 2.1 yrs, females = 3.3 ± 2.0 yrs) were recruited for the study. Multiple linear regression (MLR) models were developed for total sample and for each sex independently that only included variables that were significantly correlated to self-selected cadence. A variance inflation factor (VIF) assessed multicollinearity of variables. If VIF≥ 5, variable(s) were removed and the MLR analysis was conducted again., Results: For all models, VIF was > 5 between speed and normalized stride length, therefore we removed normalized stride length from all models. Only leg length and speed were significantly correlated (p < .001) with cadence in the regression models for total sample (R 2 = 51.9 %) and females (R 2 = 48.2 %). The regression model for all participants was Cadence = -1.251 *Leg Length + 3.665 *Speed + 254.858. The regression model for females was Cadence = -1.190 *Leg Length + 3.705 *Speed + 249.688. For males, leg length, cadence, and running experience were significantly predictive (p < .001) of cadence in the model (R 2 = 54.7 %). The regression model for males was Cadence = -1.268 *Leg Length + 3.471 *Speed - 1.087 *Running Experience + 261.378., Significance: Approximately 50 % of the variance in cadence was explained by the individual's leg length and running speed. Shorter leg lengths and faster running speeds were associated with higher cadence. For males, fewer years of running experience was associated with a higher cadence., Competing Interests: Conflicts of interest The authors have no personal, professional, or financial conflicts of interest to disclose., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Runners and coaches are often interested in identifying the "ideal" running form to reduce the risk of injury and improve performance. While differences in pelvis and hip motion have been reported among adolescent female and male long-distance runners of different stages of physical maturation, the influence of sex and/or maturation on temporal-spatial parameters is unknown for adolescent runners. Adolescent runners of different stages of physical maturation (pre-, mid-, post-pubertal) completed an overground running analysis at a self-selected speed. We performed 2 × 3 ANCOVAs (covariate = running speed) to compare temporal-spatial parameters among sex and maturation groups. Pre-adolescents ran with higher cadences and shorter step lengths than mid- ( p ≤ .01) and post-pubertal adolescents ( p ≤ .01), respectively. Mid-pubertal males and post-pubertal females also ran with higher cadences and shorter step lengths than post-pubertal males ( p ≤ .01). When step length was normalized to leg length, less physically mature runners demonstrated longer normalized step lengths ( p ≤ .01). Caution is advised when using a "one-size-fits-all" approach for recommending an "ideal" cadence and/or step length for adolescent long-distance runners. A runner's sex, stage of physical maturation and leg length should be considered when assessing and prescribing cadence and/or step length.

Background: The single-leg squat (SLS) is often used to measure two-dimensional frontal plane motion; however, there is a variability in the SLS depth across studies., Research Question: Are knee abduction (KABD), hip adduction (HADD), pelvic drop (PD), and lateral trunk flexion (LTF) angles different at greater knee flexion angles during a SLS?, Methods: Twenty pain-free females (age=22.3 ± 1.1 years, height=1.68 ± 0.06 m, mass=63.1 ± 11.7 kg) participated in this cross-sectional study. Participants performed five SLSs to the lowest depth comfortable, keeping pace with a metronome, while being video recorded in the frontal and sagittal planes. The middle three SLSs were used for analysis. KABD, HADD, PD, and LTF angles were measured at 30º, 45º, 60º, 75º, and 90º of knee flexion using extracted images. Linear mixed model analyses were used to compare across knee flexion angles and clinical significance was determined by comparing angle changes to the standard error of measurement (SEM)., Results: We observed significant differences for KABD (F=14.69, p < .001), HADD (F=46.29, p < .001), and PD (F=27.27, p < .001) among knee flexion angles. Post-hoc analyses revealed that KABD significantly increased at every increase of knee flexion angle (p ≤ .05, d=0.54-1.95), as did HADD (p ≤ .05, d=0.64-3.85) and PD (p ≤ .05, d=0.61-3.03). Changes in KABD, HADD, and PD often exceeded SEM for all changes in knee flexion angles., Significance: Knee, hip, and pelvic frontal plane motions are influenced by knee flexion angles during 2D analysis of a SLS task. Our results highlight the importance of standardizing SLS depth during research and clinical practice to ensure appropriate comparisons across measurements., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Context: Running programs traditionally monitor external loads (eg, time and distance). Recent efforts have encouraged a more comprehensive approach to also account for internal loads (eg, intensity, measured as the session rating of perceived exertion [sRPE]). The combination of external and internal loads accounts for the possible interaction between these loads. Although weekly changes in training loads have been reported between external loads and the combination of external and internal loads during 2- and 4-week training cycles, no authors have indicated whether these differences occur during an entire cross-country season in high school runners., Objective: To compare changes in training loads, as measured by (1) external loads and (2) combined external and internal loads in high school runners during an interscholastic cross-country season., Design: Case series., Setting: Community-based setting with daily online surveys., Patients or Other Participants: Twenty-four high school cross-country runners (females = 14, males = 10, age = 15.9 ± 1.1 years, running experience = 9.9 ± 3.2 years)., Main Outcome Measure(s): Week-to-week percentage changes in training load were measured by external loads (time, distance) and combined external and internal loads (time × sRPE [timeRPE] and distance × sRPE [distanceRPE])., Results: Overall, the average weekly change was 7.1% greater for distanceRPE than for distance (P = .04, d = 0.18). When the weekly running duration decreased, we found the average weekly change was 5.2% greater for distanceRPE than for timeRPE (P = .03, d = 0.24). When the weekly running duration was maintained or increased, the average weekly change was 10% to 15% greater when external and internal loads were combined versus external loads alone, but these differences were nonsignificant (P = .11-.22, d = 0.19-0.34)., Conclusions: Progression in the training load may be underestimated when relying solely on external loads. The interaction between internal loads (sRPE) and external loads (distance or time) appears to provide a different measure of the training stresses experienced by runners than external loads alone., (© by the National Athletic Trainers' Association, Inc.)

Objective: Patellofemoral pain (PFP) is a common musculoskeletal condition, which has a negative effect on physical activity and function. Currently, it is unknown how and why individuals with PFP modify their physical activity. The purpose of this qualitative study was to explore the experience of knee pain on physical activity and everyday life in individuals experiencing PFP., Design: Qualitative phenomenological interview study., Setting: University., Participants: Sixteen patients experiencing PFP., Main Outcome Measures: Semi-structured interviews were used to explore the pain experience on physical activity and daily living., Results: Patients with PFP attempted various strategies to remain physically active, such as identifying pain thresholds, activity modification, and pushing through their pain. Despite these various strategies to stay active, pain influenced their social life and patients demonstrated both fear avoidance beliefs and pain catastrophizing. Patients with PFP also reported barriers to seek care for their knee pain, such as negative past experiences with health care professionals and care not aligned with the best evidence available., Conclusion: Clinicians treating PFP should be aware of biologic, psychological, and social aspects when evaluating and intervening with patients., Competing Interests: Declaration of competing interest None declared., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Purpose: Running programs are designed to progress training loads by manipulating the duration, frequency, and/or intensity of running sessions. While some studies use journals to monitor training load, others have used wearable technology. The purpose of this study was to compare the validity of self-reported and global positioning system (GPS)-watch-derived measures of external and internal loads in high school cross-country runners., Methods: Twenty-two high school cross-country runners participated in the study during fall 2020. Participants recorded running sessions using a GPS watch and self-reported the running session using an electronic journal. External (distance and duration) and internal loads (session rating of perceived exertion [sRPE], average, and maximum heart rate) were retrieved from the GPS watch and electronic journal. Correlations compared relationships, and Bland-Altman plots compared agreements between GPS-watch-derived and self-reported measures of training loads., Results: We found moderate relationships between self-reported and GPS-watch-derived measures of external loads (distance: r = .76, moving duration: r = .74, and elapsed duration: r = .70) and poor relationships between internal loads (sRPE vs average heart rate: ρ = .11, sRPE vs maximal heart rate: ρ = .13). We found mean differences of -0.8 km (95% = -6.3 to +4.8 km) for distance, -4.5 minutes (95% = -27.8 to +33.2 min) for moving duration, and 2.7 minutes (95% = -27.8 min to +33.2 min) for elapsed duration., Conclusions: High school runners overreported running distance and duration using self-reports, and self-reported and GPS-watch-derived measures of internal loads demonstrated poor agreement. Coaches and clinicians should use caution when comparing results from studies using different methods of monitoring training loads.

Objectives: To compare beliefs of physical therapists (PTs) who read the clinical practice guideline (CPG) for the management of individuals with patellofemoral pain (PFP) to those who have not read the CPG., Design: Cross-sectional study., Setting: Online survey., Participants: 494 currently licensed/registered PTs or physiotherapists., Main Outcome Measures: Respondents answered Likert-based or open-ended questions regarding the diagnosis, prognosis, risk factors, and management of individuals with PFP, as well as confidence for managing individuals with PFP, especially the ability to identify beneficial and non-beneficial interventions. We dichotomized responses into participants who read (READERS) and did not read (NonREADERS) the CPG., Results: Most respondents held inaccurate beliefs about risk factors and prognosis; however, READERS' beliefs better aligned with the CPG than NonREADERS (P < 0.01). Most respondents correctly agreed that hip and knee exercise was the recommended treatment strategy; yet NonREADERS believed in implementing unsupported passive treatments (P < 0.01). READERS reported greater confidence in managing individuals with PFP, delivering evidence-based interventions, identifying less beneficial treatments, and locating evidence-based resources than NonREADERS (P < 0.01)., Conclusion: While READERS and NonREADERS held accurate beliefs for exercise-based treatment for PFP, greater knowledge translation is needed to counter inaccurate beliefs regarding risk factors, prognostic factors, and passive treatments., Competing Interests: Declaration of competing interest The authors have no conflicts of interest, including financial or endorsement relationships, to declare., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Objectives: Patellofemoral pain (PFP) is a common lower extremity condition that results in pain during functional tasks. Currently, it is unknown the extent to which differences in pain levels exist in individuals with PFP compared to asymptomatic controls during functional task and if pain differ across various functional tasks. The purpose of this systematic review and meta-analysis is to evaluate pain levels between individuals with PFP and asymptomatic controls and compare pain severity across various functional tasks., Design: Systematic review., Methods: OVID, SPORTSDiscus, CINAHL, Web of Science and Embase were searched for studies that included PFP and asymptomatic controls with pain assessed during a functional task. Pooled pain scores mean with 95% confidence intervals were calculated between groups across 11 functional tasks. Standardized mean differences (SMD) were calculated based on Hedge's g effect sizes. Tasks whose SMD 95% confidence intervals were non-overlapping were considered significantly different., Results: 28 articles were included for data analysis. Pain was greater across 10 tasks (SMD = 1.52-6.08) in individuals with PFP compared to the asymptomatic controls with an average SMD of 2.45. Running and star excursion balance testing resulted in greater pain than walking. Limited evidence showed greater pain in sitting than seven other tasks., Conclusions: Moderate evidence exists for greater pain levels in individuals with PFP compared to asymptomatic controls in functional tasks. Pain was greater during running and star excursion balance compared to walking. Clinicians should assess knee pain before and after functional tasks to improve our understanding of patient specific pain experiences., (Copyright © 2022 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

Background: Studies have found no or minimal differences in running kinematics between flexible and inflexible adult runners. The interaction between hamstring flexibility and running kinematics has not been reported in adolescent long-distance runners., Research Question: Does hamstring flexibility influence running kinematics in adolescent long-distance runners?, Methods: Adolescent long-distance runners (n = 140, ages 9-19) were enrolled in our cross-sectional study. Hamstring flexibility was assessed with the forward bending Beighton task. Runners were categorized if they tested positive or negative on the forward bending task. Participants ran at a comfortable self-selected speed on a treadmill. Runners who tested positive on the forward bending task (n = 17) were matched with runners who tested negative on the task (n = 17) according to sex, physical maturation, and running speed. Statistical parametric mapping compared trunk, pelvis, hip, and knee kinematic waveforms throughout the gait cycle and independent sample t tests compared temporal-spatial parameters between the groups., Results: Runners who tested positive on the forward bending task demonstrated significantly greater anterior pelvic tilt during stance (average difference = 4.8° ± 0.4°, p < .001) and swing (average difference = 4.3° ± 0.2°, p < .01) compared to runners who tested negative on the forward bending task. No significant differences were found between groups for the remaining kinematic waveforms or for any temporal-spatial parameters (p > .05)., Significance: This is the first study to report the interaction between hamstring flexibility and running kinematics in adolescent long-distance runners. The greater anterior pelvic tilt demonstrated by runners with greater hamstring flexibility may place more eccentric demands on the hamstring musculature. However, as there were no other differences in joint kinematics or temporal-spatial parameters between groups, greater hamstring flexibility does not appear to have a significant interaction with running kinematics when running at sub-maximal speeds. Our results suggest hamstring flexibility does not predispose adolescent long-distance runners to sub-optimal segment positions associated with running-related injuries., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Objectives: This study aimed to investigate differences in stance phase pelvic and hip running kinematics based on maturation and sex among healthy youth distance runners., Design: Cross-Sectional., Methods: 133 uninjured youth distance runners (M = 60, F = 73; age = 13.5 ± 2.7 years) underwent a three-dimensional running analysis on a treadmill at a self-selected speed (2.8 ± 0.6 m·s -1 ). Participants were stratified as pre-pubertal, mid-pubertal, or post-pubertal according to the modified Pubertal Maturational Observation Scale. Stance phase pelvis and hip range of motion (RoM) and peak joint positions were extracted. Two-way ANCOVAs (sex, maturation; covariate of running velocity) were used with Bonferroni-Holm method to control for multiple comparisons with a target alpha level of 0.05., Results: A two-way interaction between sex and maturation was detected (p = 0.009) for frontal plane pelvic obliquity RoM. Post-hoc analysis identified a maturation main effect only among females (p˂0.008). Pelvic obliquity RoM was significantly greater among post-pubertal (p = 0.001) compared to pre-pubertal females. Significant main effects of sex (p = 0.02), and maturation (p = 0.01) were found for hip adduction RoM. Post-hoc analysis indicated a significant increase in hip adduction RoM from pre-pubertal to post-pubertal female runners (p = 0.001). A significant main effect of sex was found for peak hip adduction angle (p = 0.001) with female runners exhibiting greater maximum peak hip adduction compared to males., Conclusions: Maturation influences pelvic and hip kinematics greater in female than male runners. Sex differences became more pronounced during later stages of puberty. These differences may correspond to an increased risk for running-related injuries in female runners compared to male runners., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Individuals with patellofemoral pain (PFP) experience discomfort during various functional activities. Long-term pain is a common consequence of PFP, yet little is known about daily pain variability. Our study consisted of 25 individuals with PFP who completed the Anterior Knee Pain Scale (AKPS) and recorded their daily pain over 10 days. Pain was evaluated using 2 measures of intensity (baseline pain, 10-day average pain) and 2 measures of variability (mean square of successive differences, probability of acute change). Associations between AKPS and the 4 pain measures were calculated with Pearson correlations. We calculated a linear regression to examine the amount of variance in the AKPS explained by the 4 pain measures. Greater mean square of successive differences values were moderately associated with lesser AKPS scores (r = -0.648, P < .001). Mean square of successive differences and 10-day averaged pain were the strongest predictors of AKPS (R2 = 0.565, P < .001). Pain variability provided a unique perspective on the pain experience and predicted patient-oriented function in individuals with PFP., (© by the National Athletic Trainers' Association, Inc.)

Context: Patellofemoral pain (PFP) is prevalent and challenging to manage. Most patients with PFP are unsatisfied with their knee function at 6 months after treatment and report ongoing pain up to 16 years after diagnosis. The confidence and knowledge of athletic trainers (ATs) in providing evidence-based care to people with PFP is unknown., Objective: To investigate the confidence and knowledge of ATs in the diagnosis, risk factors, prognosis, and treatment with current evidence for PFP., Design: Cross-sectional study., Setting: Online survey., Patient or Other Participants: A random sample of 3000 ATs were invited to participate; 261 completed the survey (10% participation rate, 88% completion rate)., Main Outcome Measures(s): We surveyed AT demographics, confidence in PFP management, and knowledge related to diagnosis, risk factors, prognosis, and treatment. The confidence and knowledge of ATs in managing PFP was assessed. Their beliefs about evidence were compared with the available evidence (ie, consensus statements, position statements, systematic reviews)., Results: Of the ATs surveyed, 91% were confident that their management of PFP aligned with the current evidence, but only 59% were confident in identifying risk factors for PFP development. In addition, 91% to 92% of ATs agreed that quadriceps and hip muscle weakness were risk factors for PFP, which aligns with the current evidence for the former but not the latter. Moreover, 93% to 97% of ATs' responses related to therapeutic exercise aligned with current evidence. However, 35% to 48% supported the use of passive treatments, such as electrophysical agents and ultrasound, which did not align with the current evidence., Conclusions: Most ATs were aware of supporting evidence for therapeutic exercise in PFP management and were confident providing it, creating a strong foundation for evidence-based care. However, varying levels of awareness of the evidence related to risk factors and passive treatments for PFP highlight the need for professional development initiatives to better align ATs' knowledge with the current evidence., (© by the National Athletic Trainers' Association, Inc.)

Running-related injuries are prevalent in adolescent long-distance runners. The aim of our retrospective study was to compare differences in sport specialization, running habits,quality of life, and sleep habits among middle-and high-school long-distance runners of different injury statuses. Middle- and high-school long-distance runners across the United States were recruited via cross-country coaches and athletic directors between January and May 2020. Participants completed an online survey with questions related to demographics, sport specialization, running habits, quality of life, sleep, and self-reported injury history. Overall, 306 participants completed the survey (male = 107, female = 176, unspecified = 23; age = 15.7 ± 1.1 years). Of the participants, 178 (58.2%) reported no history of injury, 101 (33.0%) reported a previous injury, and 27 (8.8%) reported a current injury. Middle- and high-school runners with a current injury reported significantly lower overall health ( p = .01) and average distance per run ( p = .05) than uninjured runners. No significant differences were found among injury status and sport specialization level, quality of life, sleep habits, or running volume ( p > .05). Runners with a self-reported previous or current injury do not appear to be classified as high-specialized runners more frequently than uninjured runners.

Context: Arthrogenic muscle inhibition (AMI) is a common neurophysiological response to joint injury. While athletic trainers (ATs) are constantly treating patients with AMI, it is unclear how clinicians are using the available evidence to treat the condition., Objective: To investigate ATs' general knowledge, clinical practice, and barriers for treating AMI., Methods: A cross-sectional web-based survey was utilized. The survey was distributed to a random sample of 3000 ATs from the National Athletic Trainers' Association and through social media. 143 board certified ATs (age: 34.6 [10.3] y; experience: 11.7 [9.8] y) from various clinical settings and educational backgrounds were included in the analysis., Results: One hundred one respondents were able to correctly identify the definition of AMI. The majority of these respondents correctly reported that joint effusion (n = 95, 94.1%) and abnormal activity from joint receptors (n = 91, 90.1%) resulted in AMI. Of the 101 respondents, only 58 (57.4%) reported using disinhibitory interventions to treat AMI. The most frequently used evidence supported interventions were transcutaneous electrical nerve stimulation (n = 38, 65.5%), neuromuscular electrical stimulation (n = 33, 56.9%), and focal joint cooling (n = 25, 43.1%). The interventions used correctly most often based on current evidence were neuromuscular electrical stimulation (n = 29/33, 87.9%) and transcutaneous electrical nerve stimulation (n = 26/38, 68.4%). Overall, difficulty quantifying AMI (n = 62, 61.24%) and lack of education (n = 71, 76.2%) were most frequently perceived as barriers. Respondents that did not use disinhibitory interventions perceived lack of experience treating AMI, understanding the terminology, and access to therapeutic modalities more often than the respondents that reported using disinhibitory interventions., Conclusion: Further education about concepts and treatment about AMI is warranted for ATs. Continued understanding of ATs' clinical practice in regard to AMI may help identify gaps in athletic training clinical education.

Objectives: Increased tibial axial acceleration and reduced shock attenuation are associated with running injuries and are believed to be influenced by surface type. Trail running has increased in popularity and is thought to have softer surface properties than paved surface, but it is unclear if trail surfaces influence tibial acceleration and shock attenuation. The purpose of this study was to investigate peak triaxial and resultant tibial acceleration as well as axial and resultant shock attenuation among dirt, gravel, and paved surfaces., Design: Fifteen recreational runners (12 females, 3 males, age=27.7±9.1 years) ran over dirt, gravel, and paved surfaces in a trail environment while instrumented with triaxial tibial and head accelerometers., Methods: Differences between tri-planar peak tibial accelerations (braking, propulsion, axial, medial, lateral, and resultant) and shock attenuations (axial and resultant) among surface types were assessed with one-way ANOVAs with Bonferroni post-hoc tests., Results: No significant differences were found for tibial accelerations or shock attenuations among surface types (p>0.05)., Conclusions: Dirt and gravel trail running surfaces do not have lower tibial accelerations or greater shock attenuation than paved surfaces. While runners are encouraged to enjoy the psychological benefits of trail running, trail surfaces do not appear to reduce loading forces associated with running-related injuries., (Copyright © 2021 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

Objectives: To compare trunk muscle endurance among females and males with and without patellofemoral pain (PFP), and to investigate the correlations between trunk muscle endurance and performance of the single leg hop test (SLHT) and forward step-down test (FSDT)., Design: Cross-sectional., Setting: Laboratory-based study., Participants: 110 females and 38 males with PFP, 61 females and 31males without PFP., Main Outcome Measures: Anterior and lateral trunk muscle endurance were assessed with the prone and bilateral side-bridge tests, respectively. Performance during the SLHT and FSDT was also assessed., Results: Lower anterior and lateral trunk muscle endurance were identified in females (p < .001; d = -0.74 to -0.86), but not in males (p ≥ .806; d = -0.04 to 0.05) with PFP as compared to sex-matched controls. Moderate to large, positive correlations between anterior and lateral trunk muscle endurance with performance in the SLHT and FSDT were identified in females (r = .27 to .50; p < .004) and males (r = 0.27 to 0.59; p < .031) with PFP and females without PFP (r = 0.26 to 0.40; p < .044)., Conclusion: Our findings highlight that assessing trunk muscle endurance is advised in females with PFP. Trunk muscle endurance of individuals with PFP may have a role in the performance of hopping and stepping down tasks., Competing Interests: Declaration of competing interest None declared., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Patellofemoral pain is a common and often debilitating musculoskeletal condition. Clinical translation and evidence synthesis of patellofemoral pain research are compromised by heterogenous and often inadequately reported study details. This consensus statement and associated checklist provides standards for REPORTing of quantitative PatelloFemoral Pain (REPORT-PFP) research to enhance clinical translation and evidence synthesis, and support clinician engagement with research and data collection. A three-stage Delphi process was initiated at the 2015 International Patellofemoral Research Network (iPFRN) retreat. An initial e-Delphi activity (n=24) generated topics and items, which were refined at the 2017 iPFRN retreat, and voted on prior to and following the 2019 iPFRN retreat (n=51 current and past retreat participants). Voting criteria included 'strongly recommended' (essential), 'recommended' (encouraged) and uncertain/unsure. An item was included in the checklist if ≥70% respondents voted 'recommended'. Items receiving ≥70% votes for 'strongly recommended' were labelled as such. The final REPORT-PFP checklist includes 31 items (11 strongly recommended, 20 recommended), covering (i) demographics (n=2,4); (ii) baseline symptoms and previous treatments (n=3,7); (iii) outcome measures (2,4); (iv) outcomes measure description (n=1,2); (v) clinical trial methodology (0,3) and (vi) reporting study results (n=3,0). The REPORT-PFP checklist is ready to be used by researchers and clinicians. Strong stakeholder engagement from clinical academics during development means consistent application by the international patellofemoral pain research community is likely. Checklist adherence will improve research accessibility for clinicians and enhance future evidence synthesis., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Purpose: The COVID-19 pandemic impacted the sporting and exercise activities of millions of youth. Running is an activity that could be maintained while social distancing restrictions were implemented during the pandemic. However, a recent study has indicated that youth runners reported lower running distance, frequency, and intensity during COVID-19. The reason for this reduction and the impact on overall well-being is unknown. Therefore, the purpose of this study was to determine if the social distancing restrictions during the 2020 COVID-19 pandemic influenced running motives, socialization, wellness and mental health in youth long-distance runners. Methods: A customized, open online questionnaire was provided to runners 9-19 years of age who participated in long-distance running activities including team/club cross-country, track and field (distances ≥800 m), road races, or recreational running. Participants responded to questions about demographics, motive for running, and wellness (sleep quality, anxiety, running enjoyment, food consumption quality) 6-months before as well as during social distancing restrictions due to COVID-19. Wilcoxon signed rank tests compared differences for ratio data and Chi-square tests were used to compare proportions before and during COVID-19 social distancing restrictions. Statistical significance was set at p ≤ 0.05. Results: A total of 287 youth long-distance runners (male = 124, female = 162, unspecified = 1; age = 15.3 ± 1.7 years; running experience = 5.0 ± 2.3 years) participated. Compared to their pre-COVID-19 responses, youth long-distance runners reported lower overall motivation to run ( p < 0.001) and changes to most motive rankings ( p < 0.001 to p = 0.71). The proportion of youth running alone increased during COVID-19 (65.8%) compared to pre-COVID-19 (13.8%, p < 0.001). Youth long-distance runners also reported less running enjoyment ( p = 0.001), longer sleep duration ( p < 0.001), lower sleep quality ( p = 0.05), more anxiety ( p = 0.043), and lower food quality consumed ( p < 0.001) during COVID-19 social distance restrictions. Conclusion: The COVID-19 social distancing restrictions resulted in significant decreases in motivation and enjoyment of running. The removal of competition and team-based interactions likely had a role in these decreases for this population. Continuing team-based activities (e.g., virtual) during social distancing may help with maintaining motivation of youth long-distance runners. Reduced running occurred concurrently with reduced overall well-being of youth long-distance runners during the COVID-19 pandemic., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Bazett-Jones, Garcia, Taylor-Haas, Long, Rauh, Paterno and Ford.)

Context: Previous reports suggested that highly specialized adolescent athletes may be at a higher risk of injury, worse sleep quality, and less sport enjoyment than low-level specialized athletes. To date, the sport specialization literature has primarily addressed adolescent athletes in a variety of sports. However, whether the findings on sport specialization in predominantly nonrunning athletes are generalizable to adolescent long-distance runners is unknown., Objective: To compare injury history, running volume, quality of life, sleep habits, and running enjoyment among male and female middle school and high school long-distance runners at different sport specialization levels., Design: Cross-sectional study., Setting: Online survey., Patients or Other Participants: A total of 102 male (age = 15.8 ± 0.9 years) and 156 female (age = 15.6 ± 1.4 years) uninjured middle school and high school athletes who participated in long-distance running activities (completion rate = 50.7%)., Main Outcome Measure(s): Participants were stratified by sex and sport specialization level (low, moderate, or high). Group differences were assessed in self-reported running-related injuries, running habits, EQ-5D-Y quality of life, Pittsburgh Sleep Quality Index sleep quality, sleep duration, and running enjoyment., Results: Highly specialized male and female middle school and high school long-distance runners reported more months of competition per year (P < .001), higher weekly run distance (P < .001), more runs per week (P < .001), higher average distance per run (P < .001), and greater running enjoyment (P < .001) than low-level specialized runners. Adolescent boys reported a higher average weekly run distance (P = .01), higher average distance per run (P = .01), and better sleep quality (P = .01) than adolescent girls. No differences among sport specialization levels were found for running-related injuries (P = .25), quality of life (P = .07), sleep quality (P = .19), or sleep duration (P = .11) among male or female middle school and high school runners., Conclusions: Highly specialized male and female middle school and high school long-distance runners reported higher running volumes and running enjoyment than low-level specialized runners. However, high-level specialized runners did not describe a greater number of running-related injuries, lower quality of life, or lower sleep quality or duration as expected., (© by the National Athletic Trainers' Association, Inc.)

Objectives: To compare trunk and knee biomechanics of women with and without patellofemoral pain (PFP) and knee crepitus during stair ascent., Design: Cross-sectional., Setting: Laboratory-based study., Participants: 29 women with PFP and knee crepitus (PFP Crepitus ); 28 women with PFP and no knee crepitus (PFP NOCrepitus ); 17 pain-free women with knee crepitus (Pain-free Crepitus ); and 29 pain-free women without knee crepitus (Pain-free NOCrepitus )., Main Outcome Measures: Peak trunk flexion, peak knee flexion, mean knee angular velocity, knee extensor moment at peak knee flexion, peak and impulse of the knee extensor moment., Results: PFP Crepitus group performed the stair ascent task with reduced peak knee flexion compared to Pain-free Crepitus (p = 0.04; Effect size = -0.85) and Pain-free NOCrepitus (p = 0.03; Effect size = -0.75). No significant differences among groups were found for peak trunk flexion (p = 0.979), knee angular velocity (p = 0.420), knee extensor moment at peak knee flexion (p = 0.933), peak (p = 0.290) and impulse (p = 0.122) of the knee extensor moment., Conclusion: Women with concomitant PFP and knee crepitus demonstrated reduced knee flexion during stair ascent, but no significant differences for trunk flexion and knee extensor moment variables were found., Competing Interests: Declaration of competing interest None declared., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Context: Hip muscle strength has previously been evaluated in various sagittal plane testing positions. Altering the testing position appears to have an influence on hip muscle torque during hip extension, abduction, and external rotation. However, it is unknown how altering the testing position influences hip muscle activity during these commonly performed assessments., Objectives: To evaluate how hip sagittal plane position influences hip muscle activation and torque output., Study Design: Cross-sectional., Setting: Laboratory., Patients or Other Participants: A total of 22 healthy females (age = 22.1 [1.4] y; mass = 63.4 [11.3] kg; height = 168.4 [6.2] cm) were recruited., Intervention: None., Main Outcome Measures: Participants completed isometric contractions with surface electromyography on the superior and inferior gluteus maximus; anterior, middle, and posterior gluteus medius; biceps femoris, semitendinosus, adductor longus, and tensor fascia latae. Extension and external rotation were tested in 0°, 45°, and 90° of hip flexion and abduction was tested in -5°, 0°, and 45° of hip flexion. Repeated-measures analysis of variances were used for statistical analysis (P ≤ .01)., Results: Activation of gluteal (P < .007), semitendinosus (P = .002), and adductor longus (P = .001) muscles were lesser for extension at 90° versus less flexed positions. Adductor longus activity was greatest during 90° of hip flexion for external rotation torque testing (P < .001). Tensor fascia latae (P < .001) and gluteus maximus (P < .001) activities were greater in 45° of hip flexion. Significant differences in extension (P < .001) and abduction (P < .001) torque were found among positions., Conclusions: Position when assessing hip extension and abduction torque has an influence on both muscle activity and torque output but only muscle activity for hip external rotation torque. Clinicians should be aware of the influence of position on hip extension, abduction, and external rotation muscle testing and select a position most in line with their clinical goals.

Purpose: The COVID-19 pandemic impacted the sporting and exercise activities of millions of youth. Running is an activity that could be maintained while social distancing restrictions were implemented during the pandemic. If running-related injuries do occur, these restrictions may also influence the access to care or care seeking behavior of this population. Therefore, the purpose of this study was to determine if the social distancing restrictions during the 2020 COVID-19 pandemic influenced training habits, injury, and care seeking behavior in youth long-distance runners. Methods: A customized, open online questionnaire was provided to runners 9-19 years of age who participated in long-distance running activities including team/club cross-country, track and field (distances ≥800 m), road races, or recreational running. Participants responded to questions about demographics, running habits, RRIs, and health care provider visits 6-months before as well as during social distancing restrictions due to COVID-19. Wilcoxon signed rank tests compared differences for ratio data and Chi-square tests were used to compare proportions before and during COVID-19 social distancing restrictions. Statistical significance was set at p ≤ 0.05. Results: A total of 287 youth long-distance runners (male = 124, female = 162, unspecified = 1; age = 15.3 ± 1.7 years; running experience = 5.0 ± 2.3 years) participated. Compared to their pre-COVID-19 responses, youth long-distance runners reported lower distances run per week ( p < 0.001), fewer runs per week ( p < 0.001), fewer hard runs per week ( p < 0.001), fewer number of injuries ( p < 0.001), and fewer injuries per 1,000 km ( p = 0.002) during the COVID-19 social distancing restrictions. A lower proportion of participants reported in-person health care provider visits ( p < 0.001) and a lower proportion of visits were made to an athletic trainer during COVID-19 social distancing restrictions compared to prior to COVID-19 ( p < 0.001). Conclusion: The COVID-19 pandemic resulted in significant decreases in both training and injuries which were different compared to previous reports in an adult population. Many of the runners who sustained an injury during COVID-19 social distancing restrictions did not seek care, with the most prominent reduction in visits to an athletic trainer. This could impact future injury and chronic pain., (Copyright © 2020 Bazett-Jones, Garcia, Taylor-Haas, Long, Rauh, Paterno and Ford.)

Objectives: Different angles and positions may influence the reliability and validity of hip strength dynamometry. This study examined the reliability and validity of hip strength measured with belt-stabilized handheld dynamometry (HHD) compared to isokinetic dynamometry (IKD) across multiple angles., Design: Repeated measures., Setting: Biomechanics laboratory., Participants: Thirty healthy participants completed 3 sessions., Main Outcome Measures: Hip torque was measured for hip abduction (ABD; -10°, 0°, 20°, and 40°), internal rotation (IR; -30°, -15°, 0°, 15°, and 30°), external rotation (ER; -30°, -15°, 0°, 15°, and 30°), and extension (EXT; -10°, 0°, 30°, 60°, 90°, and 120°)., Results: ABD was reliable (no intratester reliability differences p = 0.409-0.997; ICC = 0.624-0.900) and valid (no HHD-IKD difference p = 0.270-0.946; r = 0.556-0.624) measure. IR had questionable reliability (intratester reliability differences p = 0.001-0.043; ICC = 0.682-0.879) and validity (HHD-IKD differences p < 0.001; r = 0.393-0.771). ER was reliable (no intratester reliability differences p = 0.226-0.937; ICC = 0.731-0.876) but not valid (HHD-IKD differences p < 0.001-0.003; r = 0.194-0.651). EXT showed varying levels of reliability and validity; 30° was both reliable and valid. Peak torque occurred in a lengthened position for ABD, ER, and IR, and at 90° of hip flexion for EXT., Conclusions: HHD can be an effective tool for measuring strength under certain circumstances; however, IR/ER testing should be used with caution., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Musculoskeletal pain in youth is common but little is known about the influence of the number of pain sites on pain characteristics. The objective of this study was to compare pain characteristics, quality of life, sleep, sport participation between adolescents without pain, those with single site pain, and those with multi-site pain and investigate the relationship between pain duration and number of pain sites., Methods: An online survey was sent via email to 7177 possible middle- and high-school students. The students completed a survey containing questions about their pain (including location, duration, intensity, frequency), health-related quality of life, sleep quantity and quality, and sports participation. Quantitative variables were analysed with one-way ANOVAs or t-tests and qualitative variables were analysed with Pearson Chi-squared tests. Relationships were investigated with a Pearson Correlation., Results: Of the respondents (n = 1021), 52.9% reported no pain, 17.2% reported pain in a single-site, and 29.9% reported pain in multiple sites. Those with multi-site pain reported significantly lower quality of life than both pain-free youth (p < 0.001) and those with single-site pain (p < 0.001); those with single-site pain had lower quality of life than pain-free youth (p < 0.001). Those with pain reported worse sleep than those without pain (P < 0.05). No differences in sport participation were found (p > 0.10). Those with multi-site pain reported greater intensity (p = 0.005) and duration (p < 0.001) than those with single-site pain. A positive, moderate, and significant correlation (r = 0.437, p < 0.001) was found between the pain duration and number of pain sites., Conclusions: A large percentage of youth experience regular pain that affects their self-reported quality of life and sleep, with greater effects in those with multi-site pain.