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This study sought to determine if there were significant trends in lower extremity movement quality, as assessed by the Landing Error Scoring System (LESS) scores and plane-specific LESS subscales, across in 12 recent cohorts of incoming USMA cadets. prospective cohort study. United States Military Academy. 7,591. Landing Error Scoring System (LESS) scores, adjusted for sex and ACL injury history. Statistically significant inverse trends were found between total LESS score and year (p < 0.01) and sagittal plane subscale and year (p < 0.01). A statistically significant direct trend was found for the frontal/transverse plane subscale and year (p < 0.01). However, each of these trends had a small associated effect size, and none were considered clinically meaningful. There were no meaningful changes in lower extremity movement quality in incoming US Military Academy cadets between 2005 and 2017. • Stable movement quality in 7,591 US Military Academy cadets in 12 recent years. • Movement quality stability is surprising in light of recent societal trends. • These data provide the largest sample of normative LESS values to date. [ABSTRACT FROM AUTHOR]

The purpose of this article was to determine if differences in kinematic and kinetic variables observed in a double-leg screen carried over to a single-leg task. We used a case-control design with grouping based on performance during a double-leg jump landing. All participants were selected from a large university setting and testing was performed in a biomechanics laboratory. Participants were females between 18 and 25 years of age with at least high school varsity experience in one or more of the following sports: soccer, lacrosse, field hockey, rugby, basketball, or team handball. Primary outcome measures were knee angles in the frontal and sagittal planes as well as vertical ground reaction force (vGRF). There were significant between group differences in peak knee flexion and knee flexion displacement during both the double and single-leg tasks, however between group differences for peak knee valgus and knee valgus displacement noted in the double-leg task were not observed in the single-leg task. vGRF was significantly different in the single-leg task but not the double-leg task. A double leg screening may not provide complete identification of risk of injury during sports requiring single leg tasks. • Sagittal plane biomechanical errors noted during a double leg jump landing appeared to carry over to a single leg task. • Frontal plane biomechanical errors during a double leg jump landing did not appear to carry over to a single leg task. • Poor movement patterns in a double leg task correlated with greater vertical ground reaction force in a single leg landing. [ABSTRACT FROM AUTHOR]

To a) determine the acute effects of a single-dose patellar tendon isometric exercise protocol on involved limb landing biomechanics in individuals with patellar tendinopathy and asymptomatic patellar tendon pathology, and b) determine if individuals with patellar tendinopathy demonstrated changes in pain following a single-dose patellar tendon isometric exercise protocol. Single-blinded randomized cross-over trial. Laboratory; 28 young male athletes with symptomatic (n = 13, age: 19.62 ± 1.61) and asymptomatic (n = 15, age: 21.13 ± 1.88) patellar tendinopathy. Participants completed a single-dose patellar tendon isometric exercise protocol and a sham-TENS protocol, randomized and separated by 7–10 days. Pain-levels during a single-limb decline squat (SLDS) and three-dimensional biomechanics were collected during a double-limb jump-landing task before and after each intervention protocol. A mixed-model repeated measures ANOVA was conducted to compare change scores for all dependent variables. There were no group × intervention interactions for change in pain (F (1, 26) = 0.555, p = 0.463). There was one significant group × intervention interaction for vertical ground reaction force (VGRF) (F (1, 26) = 5.33, p = 0.029). However, post-hoc testing with Bonferroni correction demonstrated no statistical significance for group (SYM: t = −1.679, p = 0.119; ASYM: t = −1.7, p = 0.107) or intervention condition (isometric: t = −2.58, p = 0.016; sham-TENS: 0.72, p = 0.460). There were no further significant group × intervention interactions (p > 0.05). A single-dose patellar tendon isometric exercise protocol did not have acute effects on landing biomechanics or pain levels in male athletes with patellar tendinopathy or asymptomatic patellar tendon pathology. • A single bout of isometric exercise did not change lower extremity biomechanics during landing in male athletes with patellar tendinopathy. • Isometric exercise did not significantly increase or decrease pain levels in male athletes with low levels of patellar tendon pain. • Individualized treatment approaches for tendinopathy may be most beneficial to improve movement patterns for dynamic, sport-specific tasks. [ABSTRACT FROM AUTHOR]

Objectives: Determine the influence of movement profile on systemic stress and mechanical loading before and after high training load exposure.Design: Cross-sectional cohort study.Methods: 43 physically active, college-aged field or court sport female athletes participated in this study. Participants were assigned to a "excellent" (n=22; age=20.5±1.9yrs, height=1.67±0.67m, mass=64.5±7.8kg) or "poor" (n=21; age=20.4±1.3yrs, height=1.69±0.67m, mass=60.9±6.1kg) movement group defined by The Landing Error Scoring System. Participants completed five cycles of high training load exercise of 5-min treadmill-running at a speed coincident with 100-120% ventilatory threshold and 10 jump-landings from a 30-cm box. Jump-landing vertical ground reaction force and serum cortisol were evaluated prior to and following exercise. Vertical ground reaction force ensemble averages and 95% confidence interval waveforms were generated for pre-exercise, post-exercise, and pre-post exercise changes. A two-way mixed model ANOVA was used to evaluate the effect of movement profile on systemic stress before and after exercise.Results: There was no significant difference in changes in serum cortisol between the poor and excellent groups (p=0.69) in response to exercise. Overall, individuals in the poor group exhibited a higher serum cortisol level (p<0.05, d=0.85 [0.19,1.48]). The poor group exhibited higher magnitude vertical ground reaction force prior to (d=1.02-1.26) and after exercise (d=1.15) during a majority of the stance phase.Conclusions: Individuals with poor movement profiles experience greater mechanical loads compared to individuals with excellent movement profiles. A poor movement profile is associated with greater overall concentrations of circulating cortisol, representative of greater systemic stress. [ABSTRACT FROM AUTHOR]

Abstract Objectives Determine the association between performance on the double-leg squat (DLS) and single-leg squat (SLS) and prospective injury incidence in athletes. Design Prospective cohort study. Setting National Collegiate Athletic Association (NCAA) Division I university. Participants 111 incoming NCAA Division I athletes from 10 varsity sports teams. Main outcome measures Performance on the DLS and SLS were assessed as "poor" or "non-poor." Lower extremity (LE) injury data for the following year were extracted from electronic medical records. Multivariate Poisson regression was used to compare the incidence of LE injuries in athletes with poor versus non-poor performance on the DLS and SLS. Results The final models for the DLS and SLS were adjusted for sex and LE injury history and yielded an incidence rate ratio (IRR) of 1.33 (95% CI: 0.80 2.22) for the DLS and 1.62 (95% CI: 0.98, 2.66) for the SLS when comparing poor to non-poor movers. Conclusions Athletes with poor LE movement quality assessed on the DLS or SLS had greater incidence of LE injury than those with non-poor movement quality. This is the first study to demonstrate an association between performance on the double-leg squat and single-leg squat and injury risk in NCAA athletes. Highlights • Novel double- and single-leg squat tasks have been developed to screen athletes. • Scores on these tasks are meaningfully associated with lower extremity injury risk. • Continued development of these screening tools is recommended in larger samples. [ABSTRACT FROM AUTHOR]

Objective To determine whether anterior cruciate ligament–deficient (ACL-D) individuals and individuals with a reconstructed anterior cruciate ligament (ACL-R) rely more heavily on visual information to maintain postural control. Data Sources PubMed, CINAHL, and SPORTDiscus databases were searched from their earliest available date to May 24, 2016, using a combination of keywords. Study Selection Articles were included if they reported any instrumented static single-leg balance outcome in both a patient and control sample. The means and SDs of these outcomes must have been reported with both eyes open and eyes closed. Data Extraction Sample sizes, means, and SDs of single-leg balance measures for each group's eyes open and eyes closed testing conditions were extracted. The methodological quality of included studies was independently evaluated by multiple authors using an adapted version of the Quality Index. Data Synthesis Effect sizes were calculated by dividing the differences in change between eyes closed and eyes open in the ACL-D and control group and the ACL-R and control group by the pooled SD from the eyes closed trials for each analysis. Significant differences between the ACL-D and control group (effect size, −1.66; 95% confidence interval [CI], −2.90 to −.41) were noted. The ACL-R and control group were not different (effect size, −.61; 95% CI, −2.17 to .95). Conclusions ACL-D individuals but not individuals with ACL-R demonstrate a greater reliance on visual information during single-leg stance compared with healthy individuals. [ABSTRACT FROM AUTHOR]

Objectives Evaluate the effect of a anterior cruciate ligament injury prevention program coaching workshop on elite-level youth soccer coaches’ behavioral determinants to implement a injury prevention program and describe coaches’ subsequent injury prevention program implementation compliance. Design Descriptive study. Methods We evaluated a soccer club's coaches’ behavioral determinants regarding injury prevention programming implementation before and after a coaching workshop using pre- and post-workshop surveys. We then described the club's coaches’ subsequent adoption of and implementation compliance with the injury prevention programming during the following season. Results The injury prevention workshop increased coaches’ attitudes toward conducting a program at the beginning of practice ( p < 0.05), substituting the program for a warm-up prior to practice ( p < 0.05), and improving player cutting and landing technique by implementing the program ( p < 0.05). The injury prevention program workshop increased coaches’ perceived behavioral control; feeling more comfortable in their ability to teach their team a program ( p < 0.05), and more confident leading a program if given instructions ( p < 0.05). The injury prevention program workshop increased coaches’ intent to implement a program the next season ( p < 0.05), to implement a program for 15 min ( p < 0.05), and 20 min ( p < 0.05) prior to the start of a training session. Only 53% of the club's teams implemented the injury prevention program, with implementers demonstrating high variability in program fidelity. Conclusions Coaching workshops can effectively increase coach attitudes, perceived behavioral control, and intent to implement a injury prevention program. However, high levels of behavioral determinants do not appear to translate to high levels of implementation compliance. [ABSTRACT FROM AUTHOR]

The article discusses the steps for creating and conducting a preventive training initiative for military service members. Topics covered include an overview of the Translating Research Into Injury Prevention Practice (TRIPP) framework and the focus of the framework on preventing servicemen from being injured. Also mentioned is the development of solutions to avoid such problems.

Abstract: Forward head and rounded shoulder posture (FHRSP) is theorized to contribute to alterations in scapular kinematics and muscle activity leading to the development of shoulder pain. However, reported differences in scapular kinematics and muscle activity in those with forward head and rounded shoulder posture are confounded by the presence of shoulder pain. Therefore, the purpose of this study was to compare scapular kinematics and muscle activity in individuals free from shoulder pain, with and without FHRSP. Eighty volunteers were classified as having FHRSP or ideal posture. Scapular kinematics were collected concurrently with muscle activity from the upper and lower trapezius as well as the serratus anterior muscles during a loaded flexion and overhead reaching task using an electromagnetic tracking system and surface electromyography. Separate mixed model analyses of variance were used to compare three-dimensional scapular kinematics and muscle activity during the ascending phases of both tasks. Individuals with FHRSP displayed significantly greater scapular internal rotation with less serratus anterior activity, during both tasks as well as greater scapular upward rotation, anterior tilting during the flexion task when compared with the ideal posture group. These results provide support for the clinical hypothesis that FHRSP impacts shoulder mechanics independent of shoulder pain. [Copyright &y& Elsevier]

Abstract: Background: Movement variability may influence episodes of instability following lateral ankle sprain. Methods: Sixty-three recreational athletes with a history of moderate-severe ankle sprain were recruited. Mechanically and functionally unstable ankle groups had ⩾2 episodes of instability in the last year. Mechanically unstable had clinically lax lateral ankle ligaments; functionally unstable and copers did not. Copers had a history of sprain but no residual instability. Lower extremity 3-dimensional kinematics and ground reaction forces were measured during a 2-legged stop jump. Average ensemble curves of eight trials normalized to 100% of stance phase were created. The coefficient of variation and average standard deviation of the ensemble curves of each variable were identified. A loge (ln) transformation was performed on the data. One-way ANOVAs with Tukey post hoc testing were utilized with α =0.05. Findings: The functionally unstable group demonstrated greater mean (standard deviation) ln coefficient of variation ankle inversion/eversion 3.56 (1.19) than the mechanically unstable 2.77 (0.95) and copers 2.74 (1.05) (P =0.05 and P =0.04; =0.12), and greater ln standard deviation ankle inversion/eversion 1.07 (0.78) than copers 0.61 (0.31) ( =0.13). The mechanically unstable group demonstrated greater ln coefficient of variation anterior–posterior ground reaction force 3.69 (0.27) than functionally unstable 3.43 (0.25) (P =0.02; =0.13). Interpretation: Functionally unstable individuals demonstrated greater ankle frontal plane movement variability during a stop jump, which may increase risk of instability. Mechanically unstable participants demonstrated greater anterior–posterior ground reaction force variability, which may indicate difficulty mitigating landing forces with lax ligaments. Movement variability may influence episodes of ankle instability. [Copyright &y& Elsevier]

Abstract: Background: Chronic ankle instability commonly develops after lateral ankle sprain, but differences in movement patterns between subtypes of ankle instability have not been determined. We hypothesized mechanically and functionally unstable ankle subjects would demonstrate different kinematics and kinetics compared to a group of ankle sprain injury “copers”. Methods: Sixty-three recreational athletes, 21 in each of 3 groups (11 males, 10 females) matched for gender, age, height, mass, and limb dominance were tested. Knee and ankle sagittal and frontal plane motion, peak ground reaction forces, and time to peak ground reaction forces were measured during 5 tasks (walk, step down, run, drop jump, and stop jump). Findings: Using 5 one-way Analyses of Variance with Tukey post hoc testing at α =0.05, the mechanically unstable group displayed at least one difference in sagittal and/or frontal plane ankle motion at initial contact, maximum, and/or in displacement than the functionally unstable and coper groups in each task except the run (P <0.05). The greatest number of differences occurred in the drop jump and stop jump tasks. The mechanically unstable group exhibited greater frontal plane displacement and maximum eversion, and decreased sagittal plane displacement and maximum plantar flexion in several tasks. Interpretation: The mechanically unstable group demonstrated altered ankle motion patterns when compared to functionally unstable and coper groups. The landing pattern may help avoid ankle sprains, but may also increase risk of ankle joint degeneration. Unstable ankle groups exhibit different movement patterns and may require different treatment regimens. [Copyright &y& Elsevier]

Abstract: Bell DR, Padua DA, Clark MA. Muscle strength and flexibility characteristics of people displaying excessive medial knee displacement. Objective: To determine differences in strength and range of motion (ROM) between participants who exhibit medial knee displacement (MKD) during a squat that is corrected by a heel lift and those who do not. Design: Case control. Setting: Sports medicine research laboratory. Participants: Thirty-seven healthy subjects (control, 19; MKD, 18) with no lower-extremity injury in the past 6 months volunteered to participate. Interventions: Not applicable. Main Outcome Measures: Peak force was measured in newtons using a hand-held dynamometer and passive ROM was measured in degrees with a goniometer. Separate multivariate analyses of variance were used to determine differences in strength and ROM between groups. Post hoc testing was used to elucidate differences between groups. Results: The MKD group had the following: greater hip external rotation strength (P=.03), increased hip extension strength (P=.01), less plantarflexion strength (P=.007), and increased hip external rotation ROM (P=.008). Conclusions: The MKD group exhibited tight and weak ankle musculature. Interventions focusing on improving strength and ROM of the ankle may improve kinematics during a squat. [Copyright &y& Elsevier]

Abstract: Background: An erect posture and greater knee valgus during landing have been implicated as anterior cruciate ligament injury risk factors. While previous research suggests coupling of knee and hip kinematics, the influence of trunk positioning on lower extremity kinematics has yet to be determined. We hypothesized that greater trunk flexion during landing would result in greater knee and hip flexion and lesser knee valgus. Identification of a modifiable factor (e.g. trunk flexion) which positively influences kinematics of multiple lower extremity joints would be invaluable for anterior cruciate ligament injury prevention efforts. Methods: Forty healthy individuals completed two drop landing tasks while knee, hip, and trunk kinematics were sampled. The first task constituted the natural/preferred landing strategy (Preferred), while in the second task, subjects actively flexed the trunk upon landing (Flexed). Findings: Peak trunk flexion angle was 47° greater for Flexed compared to Preferred (P <0.001), and was associated with increases in peak hip flexion angle of 31° (P <0.001) and peak knee flexion angle of 22° (P <0.001). Interpretation: Active trunk flexion during landing produces concomitant increases in knee and hip flexion angles. A more flexed/less erect posture during landing is associated with a reduced anterior cruciate ligament injury risk. As such, incorporating greater trunk flexion as an integral component of anterior cruciate ligament injury prevention programs may be warranted. [Copyright &y& Elsevier]

Abstract: Background. Dynamic joint stability is derived, in part, from active muscle stiffness. Previous research has identified greater structural musculotendinous stiffness in males than in females, suggesting potential sex differences in joint stability. However, structural stiffness is influenced by anthropometrics, and it is currently unclear if sex differences in musculotendinous stiffness are purely functions of anthropometrics or related to additional factors. The purpose of this investigation was to compare structural stiffness and material modulus of the triceps surae between sexes to determine the relative influence of anthropometrics. It was hypothesized that males would demonstrate greater structural stiffness and material modulus. Methods. Twenty male and 20 female individuals volunteered for participation. Active triceps surae structural stiffness was estimated from the damped frequency of oscillation of the shank about the ankle. Material modulus was calculated as the ratio of stress to strain, derived from estimates of triceps surae length and physiological cross-sectional area. Findings. Structural stiffness was significantly greater in males [mean (SD)] [137.41 (26.99) N/cm] than females [91.06 (20.10) N/cm]. Similarly, material modulus was significantly greater in males [2778.51 (549.95) Pa] than females [1968.58 (439.61) Pa]. Interpretation. Greater structural stiffness in males identified in previous literature appears to be a true phenomenon. Identification of greater material modulus in males suggests that these differences are likely attributable to sex differences in tendon stiffness and muscle architecture. These results indicate that male musculature is more effective at resisting changes in its length, a finding which may have implications for joint stability. [Copyright &y& Elsevier]

Abstract: Although mean amplitude and ON–OFF timing of muscle recruitment and electromyography (EMG) activation during gait is achieved by an age of six to eight years in normally developing children, recruitment dynamics illustrated by the shape of the EMG waveform may require continued developmental practice to achieve a stable pattern. Previous analyses have quantified the repeatability of the EMG waveform in adult subjects, but EMG variability for a pediatric population may be significantly different. The goal of this study was to quantify intra-session and inter-session variability in the phasic EMG waveform patterns from the lower limb muscles during self-selected speeds of walking in healthy-normal children for comparison with adult variability in gait EMG. The variance ratio quantifies the repeatability of the integrated EMG waveform shape in a group of normally-developing children. Results reveal that between-session EMG waveform variability were similar in adult and pediatric populations, but within-session variability for the children was approximately twice the published value for adults. Clinical implications of this pediatric EMG variability suggest cautious interpretation of data from limited trial samples or inter-session changes in performance of gait data. [Copyright &y& Elsevier]

Insufficient active knee flexor stiffness may predispose the anterior cruciate ligament to injury. Insufficient passive stiffness may result in insufficient active stiffness. Similarly, higher levels of musculotendinous extensibility may inhibit active and passive muscle stiffness, potentially contributing to an increased risk of injury. The literature is both limited and inconsistent concerning relationships between extensibility, passive stiffness, and active stiffness. Extensibility was measured as the maximal active knee extension angle from a supine position with the hip flexed to 90°. Passive stiffness was calculated as the slope of the moment–angle curve resulting from passive knee extension. Active stiffness was assessed via acceleration associated with damped oscillatory motion about the knee. Stepwise multiple regression indicated that passive stiffness accounted for 25% of active muscle stiffness variance. The linear combination of extensibility and passive stiffness explained only 2% more variance compared to passive stiffness alone. Musculotendinous extensibility was moderately related to passive muscle stiffness, and weakly related to active muscle stiffness. The moderate relationship observed between active and passive stiffness emphasizes the dependence of active muscle stiffness on cross-bridge formation, and the relatively smaller contribution from parallel elastic tissues. Additionally, heightened extensibility does not appear to be a predisposing factor for reduced muscle stiffness. [Copyright &y& Elsevier]

Low-cost markerless motion capture systems offer the potential for 3D measurement of joint angles during human movement. This study aimed to validate a smartphone-based markerless motion capture system's (OpenCap) derived lower extremity kinematics during common return-to-sport tasks, comparing it to an established optoelectronic motion capture system. Athletes with prior anterior cruciate ligament reconstruction (12–18 months post-surgery) performed three movements: a jump-landing-rebound, single-leg hop, and lateral-vertical hop. Kinematics were recorded concurrently with two smartphones running OpenCap's software and with a 10-camera, marker-based motion capture system. Validity of lower extremity joint kinematics was assessed across 437 recorded trials using measures of agreement (coefficient of multiple correlation: CMC) and error (mean absolute error: MAE, root mean squared error: RMSE) across the time series of movement. Agreement was best in the sagittal plane for the knee and hip in all movements (CMC > 0.94), followed by the ankle (CMC = 0.84–0.93). Lower agreement was observed for frontal (CMC = 0.47–0.78) and transverse (CMC = 0.51–0.6) plane motion. OpenCap presented a grand mean error of 3.85° (MAE) and 4.34° (RMSE) across all joint angles and movements. These results were comparable to other available markerless systems. Most notably, OpenCap's user-friendly interface, free software, and small physical footprint have the potential to extend motion analysis applications beyond conventional biomechanics labs, thus enhancing the accessibility for a diverse range of users. [ABSTRACT FROM AUTHOR]

Abstract: Background: Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle''s resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively. Methods: Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests. Findings: Anterior tibial translation was correlated with hamstring stiffness (r =−0.538; P =0.002), but not with hamstring strength (r =−0.088; P =0.644). Hamstring stiffness and strength were not correlated (r =0.054; P =0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t 28 =2.186; P <0.037; ES=0.36), but hamstring strength did not differ between these groups (t 28 =1.057; P <0.300; ES=0.17). Interpretation: Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings’ ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs. [Copyright &y& Elsevier]

Abstract: This investigation was designed to test the validity and reliability of a new measure of inversion/eversion ankle stiffness on a unique medial/lateral swaying cradle device utilizing a test/retest with comparison to a known standard. Ankle stiffness is essential to maintaining joint stability. Most ankle injuries occur via an inversion mechanism. To date, very little information is available regarding stiffness of the evertor muscles in the prevention of excessive inversion joint rotation. Transient oscillation data representing inversion/eversion stiffness was obtained in a bipedal weight-bearing stance with an upright posture. Using commercially available springs with stiffness of 4.80N/cm the measured value recorded by the cradle was 4.87N/cm. Mean active stiffness values of the ankle were 35.70Nm/cm (SD 9.45). The trial-to-trial reliability ICC (2,1) coefficient was 0.96 with an SEM of 2.05Nm/rad, and the day-to-day reliability ICC (2,k) coefficient was 0.93 and an SEM of 3.00Nm/rad. The results demonstrate that inversion/eversion ankle stiffness measures on this device are a valid, repeatable and consistent measure. This is relevant because the ability to accurately quantify inversion/eversion ankle stiffness will improve our understanding of biomechanical stability and factors that influence it. It will also enable identification of ankle injury risk factors that will lead to more efficient rehabilitation programs and injury prevention strategies. [Copyright &y& Elsevier]

Abstract: The spinal stretch reflex (SSR) is commonly assessed via electromyographic (EMG) analysis of joint perturbations inducing changes in muscle length. Previous literature indicates that when large experimental changes in magnitude of agonist background EMG, perturbation velocity, and perturbation amplitude are employed, SSR latency and amplitude are significantly altered. The purpose of this investigation was to evaluate the relative dependence of SSR latency and amplitude on inherent variability in these experimental variables. Soleus SSR latency and amplitude were assessed in 40 healthy subjects following dorsiflexion perturbation under an active state (∼14% MVC). Experimental variables displayed limited variability (means±SD): soleus background EMG (13.47±7.08% MVC), perturbation velocity (96.1±30°/s), and perturbation amplitude (4±1°). SSR latency was not significantly related to soleus background EMG (r =0.189), perturbation velocity (r =0.213), or perturbation amplitude (r =0.202). Similarly, SSR amplitude was not significantly related to soleus background EMG (r =0.306), perturbation velocity (r =0.053), or perturbation amplitude (r =0.056). Variability in experimental variables was much smaller than what has been reported in the literature to significantly impact SSR characteristics. These results suggest that SSR latency and amplitude are independent of agonist background EMG, perturbation velocity, and perturbation amplitude when experimental variability is relatively limited. [Copyright &y& Elsevier]

Objective. To compare extensibility, and passive and active stiffness of the knee flexors between males and females.Design. An experimental design utilized 15 males and 15 females to identify sex differences in active extensibility, and active and passive stiffness of the knee flexors.Background. Muscle stiffness appears to contribute to joint stability from both mechanical and neuromuscular perspectives. Differences in knee flexor stiffness may partially explain higher female anterior cruciate ligament injury rates.Methods. Active knee flexor extensibility was assessed as subjects extend the knee from a fixed hip position, measuring the final knee position. Passive knee flexor stiffness was calculated as the slope of the moment–angle curve resulting from controlled passive knee extension. Active knee flexor stiffness was assessed by loading the lower extremity with 10% total body mass, and measuring the damping effect of the knee flexors on imposed vibratory motion about the knee joint.Results. Females displayed greater active extensibility (P<0.05), while males displayed greater active (P<0.05) and passive (P<0.05) knee flexor stiffness. Sex differences in active and passive knee flexor stiffness were not significant following normalization to anthropometric characteristics.Conclusions. The knee flexor musculature in males is less extensible and displays greater active and passive stiffness compared to females. However, these differences may be functions of greater mass and height in males.RelevanceThe increased female anterior cruciate ligament injury rate may be related to insufficient knee flexor stiffness. Heightened muscle stiffness may enhance joint stability, thus reducing the likelihood of injury and protecting healing and surgically repaired tissues. [Copyright &y& Elsevier]

Active females demonstrate increased risk for musculoskeletal injuries relative to equivalently-trained males. Although gender differences in factors such as passive laxity, skeletal geometry and kinematics have been examined, the effect of gender on active muscle stiffness has not been reported. Stiffness of the active quadriceps and hamstrings musculature were recorded during isometric knee flexion and extension exertions from twelve male and eleven female subjects. A second-order biomechanical model of joint dynamics was used to quantify stiffness from the transient motion response to an angular perturbation of the lower-leg. Female subjects demonstrated reduced active stiffness relative to male subjects at all torque levels, with levels 56–73% of the males. Effective stiffness increased linearly with the torque load, with stiffness increasing at a rate of 3.3 Nm/rad per unit of knee moment in knee flexion exertions (hamstrings) and 6.6 Nm/rad per unit of knee moment extension exertions (quadriceps). To account for gender differences in applied moment associated with leg mass, regressions analyses were completed that demonstrated a gender difference in the slope of stiffness-versus-knee moment relation. Further research is necessary to identify the cause of the observed biomechanical difference and implications for controlling injury. [Copyright &y& Elsevier]

This study examined the feasibility of workload monitoring to assess internal workload in law enforcement officers (LEO) using a multi-methodological approach. Fifty front-line LEO completed workload surveys on workdays for eight weeks. Retention and adherence were assessed across the survey period. LEO completed usability and likelihood to continue questionnaires, while departmental administrators (n = 8) received workload reports and completed utility and sustainability questionnaires. A subsample of LEO and administrators participated in semi-structured interviews, following consensual qualitative research design. LEO retention (96%), survey adherence (94%), and usability scores (88.3/100) were high, with a moderate likelihood to continue to use the survey. Administration reported high utility and sustainability. The high adherence rates and usability scores, coupled with strong administrative support, suggest that workload monitoring may be a feasible strategy among LEO to monitor occupational workloads. The LEO and administration feedback highlight areas of improvement (e.g., data transparency, departmental collaboration) to inform future implementation. [ABSTRACT FROM AUTHOR]

Abstract Background Aberrant mechanical loading during gait is hypothesized to contribute to the development of posttraumatic osteoarthritis following anterior cruciate ligament reconstruction. Our purpose was to determine if peak vertical ground reaction force and instantaneous vertical ground reaction force loading rate associate with the acute change in serum cartilage oligomeric matrix protein following a 20-minute bout of walking. Methods We enrolled thirty individuals with a unilateral anterior cruciate ligament reconstruction. Peak vertical ground reaction force and instantaneous vertical ground reaction force loading rate were extracted from the first 50% of the stance phase of gait during a 60-second trial. Blood samples were collected immediately before and after 20 min of treadmill walking at self-selected speed. The change in serum cartilage oligomeric matrix protein from pre- to post-walking was calculated. Stepwise linear regression models were used to determine the association between each outcome of loading and the change in serum cartilage oligomeric matrix protein after accounting for sex, gait speed, time since anterior cruciate ligament reconstruction, graft type, and history of concomitant meniscal procedure (ΔR2). Findings Lesser peak vertical ground reaction force (ΔR2 = 0.208; β = −0.561; P = 0.019) and instantaneous vertical ground reaction force loading rate (ΔR2 = 0.168; β = −0.519; P = 0.037) on the anterior cruciate ligament reconstructed limb associated with a greater increase in serum cartilage oligomeric matrix protein following 20 min of walking. Interpretation Mechanical loading may be a future therapeutic target for altering the acute biochemical response to walking in individuals with an anterior cruciate ligament reconstruction. Highlights • Lesser magnitude of loading associated with a greater biochemical response after walking. • Lesser instantaneous rate of loading was associated with a greater biochemical response. • Limb symmetry of loading characteristics was not associated with the biochemical response. [ABSTRACT FROM AUTHOR]

Individuals with anterior cruciate ligament reconstruction (ACLR) often exhibit a “stiffened knee strategy” or an excessively extended knee during gait, characterized by lesser knee flexion excursion and peak internal knee extension moment (KEM). The purpose of this study was to determine the effect of real-time biofeedback (RTBF) cuing an acute change in peak vertical ground reaction force (vGRF) during the first 50% of the stance phase of walking gait on: (1) root mean square error (RMSE) between actual vGRF and RTBF target vGRF; (2) perceived difficulty; and (3) knee biomechanics. Acquisition and short-term recall of these outcomes were evaluated. Thirty individuals with unilateral ACLR completed 4 separate walking sessions on a force-measuring treadmill that consisted of a control (no RTBF) and 3 experimental loading conditions using RTBF including: (1) 5% vGRF increase (high-loading), (2) 5% vGRF decrease (low-loading) and (3) symmetric vGRF between limbs. Bilateral biomechanical outcomes were analyzed during the first 50% of the stance phase, and included KEM, knee flexion excursion, peak vGRF, and instantaneous vGRF loading rate (vGRF-LR) for each loading condition. Peak vGRF significantly increased and decreased during high-loading and low-loading, respectively compared to control loading. Instantaneous vGRF-LR, peak KEM and knee flexion excursion significantly increased during the high-loading condition compared to low-loading. Perceived difficultly and RMSE were lower during the symmetrical loading condition compared to the low-loading condition. Cuing an increase in peak vGRF may be beneficial for increasing KEM, knee flexion excursion, peak vGRF, and vGRF-LR in individuals with ACLR. Clinical Trials Number: NCT03035994. [ABSTRACT FROM AUTHOR]

Background Aberrant walking-gait and jump-landing biomechanics may influence the development of post-traumatic osteoarthritis and increase the risk of a second anterior cruciate ligament injury, respectively. It remains unknown if individuals who demonstrate altered walking-gait biomechanics demonstrate similar altered biomechanics during jump-landing. Our aim was to determine associations in peak knee biomechanics and limb-symmetry indices between walking-gait and jump-landing tasks in individuals with a unilateral anterior cruciate ligament reconstruction. Methods Thirty-five individuals (74% women, 22.1 [3.4] years old, 25 [3.89] kg/m 2 ) with an anterior cruciate ligament reconstruction performed 5-trials of self-selected walking-gait and jump-landing. Peak kinetics and kinematics were extracted from the first 50% of stance phase during walking-gait and first 100 ms following ground contact for jump-landing. Pearson product-moment (r) and Spearman's Rho (ρ) analyses were used to evaluate relationships between outcome measures. Significance was set a priori ( P  ≤ 0.05). Findings All associations between walking-gait and jump-landing for the involved limb, along with the majority of associations for limb-symmetry indices and the uninvolved limb, were negligible and non-statistically significant. There were weak significant associations for instantaneous loading rate (ρ = 0.39, P  = 0.02) and peak knee abduction angle (ρ = 0.36, p  = 0.03) uninvolved limb, as well as peak abduction displacement limb-symmetry indices (ρ= − 0.39, p  = 0.02) between walking-gait and jump-landing. Interpretation No systematic associations were found between walking-gait and jump-landing biomechanics for either limb or limb-symmetry indices in people with unilateral anterior cruciate ligament reconstruction. Individuals with an anterior cruciate ligament reconstruction who demonstrate high-involved limb loading or asymmetries during jump-landing may not demonstrate similar biomechanics during walking-gait. [ABSTRACT FROM AUTHOR]

Background The purpose of this study was to determine associations between self-reported function (International Knee Documentation Committee Index), isometric quadriceps strength and rate of torque development in individuals with a unilateral anterior cruciate ligament reconstruction. Methods Forty-one individuals [31% male, BMI mean 25 (SD 4) kg/m 2 , months post anterior cruciate ligament reconstruction mean 49 (SD 40)] completed the self-reported function and isometric quadriceps function testing. Rate of torque development was assessed at 0–100 ms (early), 100–200 ms (late) ms, and peak following the onset of contraction. Associations were examined between rate of torque development, strength, and self-reported function. Linear regression was used to determine the unique amount of variance explained by the combination of rate of torque development and strength. Findings Higher rate of torque development 100–200 ms is weakly associated with higher self-reported function in individuals with a unilateral anterior cruciate ligament reconstruction (r = 0.274, p = 0.091); however, rate of torque development 100–200 ms does not predict a significant amount of variance in self-reported function after accounting for strength (ΔR 2 = 0.003, P = 0.721). Interpretation Quadriceps strength has a greater influence on self-reported function compared to rate of torque development in individuals with an anterior cruciate ligament reconstruction with time from surgery. [ABSTRACT FROM AUTHOR]

Background Alterations in mechanical loading following anterior cruciate ligament reconstruction may lead to the development of knee osteoarthritis. Feedback that cues a change in knee kinematics during walking gait may influence mechanical loading, yet it remains unknown if knee kinematics predict kinetics during walking gait. Our aim was to determine if sagittal plane knee kinematics predict kinetics during walking gait in anterior cruciate ligament reconstructed individuals. Methods Forty-one individuals with a history of primary, unilateral anterior cruciate ligament reconstruction completed a motion capture walking gait analysis. Hierarchical linear regression analyses were used in order to determine the amount of variance in the kinetic variables of interest (peak vertical ground reaction force, instantaneous and linear vertical ground reaction force loading rate) that was individually predicted by the kinematic variables of interest (knee flexion angle at heelstrike, peak knee flexion angle, and knee flexion excursion). Findings Knee flexion excursion of the injured limb significantly predicted 11% of the variance in peak vGRF of the injured limb after accounting for gait speed and peak knee flexion angle (ΔR 2 = 0.11, P = 0.004). After accounting for gait speed and knee flexion angle at heelstrike, knee flexion excursion significantly predicted 16% of the variance in the injured limb peak vertical ground reaction force (ΔR 2 = 0.16, P = 0.001). No kinematic variable predicted vertical ground reaction force loading rate. Interpretation Altering knee flexion excursion may be useful as a future therapeutic target for modifying peak vertical ground reaction force during walking gait following anterior cruciate ligament reconstruction. [ABSTRACT FROM AUTHOR]

Background: Greater total energy absorption by the lower extremity musculature during landing may reduce stresses placed on capsuloligamentous tissues with differences in joint contributions to energy absorption potentially affecting anterior cruciate ligament injury risk. However, the relationships between energy absorption and prospectively identified biomechanical factors associated with non-contact anterior cruciate ligament injury have yet to be demonstrated. Methods: Sagittal plane total, hip, knee and ankle energy absorption, and peak vertical ground reaction force, anterior tibial shear force, knee flexion and knee valgus angles, and internal hip extension and knee varus moments were measured in 27 individuals (14 females, 13 males) performing double leg jump landings. Correlation coefficients assessed the relationships between energy absorption during three time intervals (initial impact phase, terminal phase, and total landing) and biomechanical factors related to anterior cruciate ligament injury. Findings: More favorable values of biomechanical factors related to non-contact anterior cruciate ligament injury were associated with: 1) Lesser total (R 2 =0.178–0.558), hip (R 2 =0.229–0.651) and ankle (R 2 =0.280), but greater knee (R 2 =0.147) energy absorption during the initial impact phase; 2) Greater total (R 2 =0.170–0.845), hip (R 2 =0.599), knee (R 2 =0.236–0.834), and ankle (R 2 =0.276) energy absorption during the terminal phase of landing; and 3) Greater knee (R 2 =0.158–0.709), but lesser hip (R 2 =0.309) and ankle (R 2 =0.210–0.319) energy absorption during the total landing period. Interpretation: These results suggest that biomechanical factors related to anterior cruciate ligament injury are influenced by both the magnitude and timing of lower extremity energy absorption during landing. [Copyright &y& Elsevier]

Abstract: Gender has been identified as a risk factor for non-contact anterior cruciate ligament (ACL) injuries. Although some possible biomechanical risk factors underlying the gender differences in the risk for non-contact ACL injuries have been identified, they have not been quantitatively confirmed yet because of the descriptive nature of the traditional epidemiological methods. The purpose of this study was to validate a stochastic biomechanical model for the risk and risk factors for non-contact ACL injuries. An ACL loading model was developed and instrumented to a Monte Carlo simulation to estimate the ACL injury rate for a stop–jump task in which non-contact ACL injuries frequently occur. Density distributions of independent variables of the ACL loading model were determined from in-vivo data of 40 male and 40 female athletes when performing the stop–jump task. A non-contact ACL injury was defined as the peak ACL loading being greater than 2250N for males and 1800N for females. The female-to-male non-contact ACL injury rate ratio was determined as the ratio of the probability of ACL ruptures of females to that of males. The female-to-male non-contact ACL injury rate ratio predicted by the stochastic biomechanical model was 4.96 (SD=0.22). The predicted knee flexion angle at the peak ACL loading in the simulated injury trials was 22.0 (SD=8.0) degrees for males and 24.9 (SD=5.6) degrees for females. The stochastic biomechanical model for non-contact ACL injuries developed in the present study accurately predicted the female-to-male injury rate ratio for non-contact ACL injuries and one of the kinematic characteristics of the injury. [Copyright &y& Elsevier]

Abstract: Background: Eccentric quadriceps contraction during landing and the resulting anterior tibial shear force are anterior cruciate ligament injury risk factors, while hamstring contraction limits anterior cruciate ligament loading. Anterior tibial shear force is derived from quadriceps and hamstring co-contraction, and a greater quadriceps/hamstring strength ratio has been associated with heightened lower extremity injury risk. The purpose of this investigation was to evaluate relationships between anterior tibial shear force during landing and quadriceps and hamstring strength. Methods: Anterior tibial shear force was calculated during a jump landing task in 26 healthy females. Isokinetic eccentric quadriceps strength and concentric hamstrings strength were assessed at 60°/s, 180°/s, and 300°/s. Correlational analyses were conducted to evaluate relationships between lower extremity strength and anterior tibial shear force. Findings: Quadriceps (r =0.126 to 0.302, P >0.05) and hamstrings strength (r =−0.019 to 0.058, P >0.05) and the quadriceps/hamstring ratio (r =0.036 to 0.127, P >0.05) were not significant predictors of anterior tibial shear force. Interpretation: Quadriceps and hamstring strength are not indicative of sagittal-plane knee loading during landing. Contractile force resulting from maximal strength testing may not represent that produced during landing, as it is unlikely that landing requires maximal effort. Additionally, peak anterior tibial shear force, quadriceps torque, and hamstrings torque are generated at different points in the knee flexion/extension range of motion. Therefore, peak anterior tibial shear force is a function of the available strength at a given point in the range of motion rather than of peak strength. These findings illustrate the limitations of peak strength values in predicting dynamic loading during landing. [Copyright &y& Elsevier]

We aimed to determine the effect of cueing an increase or decrease in the vertical ground reaction force impact peak (peak in the first 50% of stance) on vertical ground reaction force, knee flexion angle, internal knee extension moment, and internal knee abduction moment waveforms throughout stance in individuals 6–12 months after an anterior cruciate ligament reconstruction. Twelve individuals completed 3 conditions (High, Low, and Control) where High and Low Conditions cue a 5% body weight increase or decrease, respectively, in the vertical ground reaction force impact peak compared to usual walking. Biomechanics during High and Low Conditions were compared to the Control Condition throughout stance. The High Condition resulted in: (a) increased vertical ground reaction forces at each peak and decreased during mid-stance, (b) greater knee excursion (i.e., greater knee flexion angle in early stance and a more extended knee in late stance), (c) greater internal extension moment for the majority of stance, and (d) lesser second internal knee abduction moment peak. The Low Condition resulted in: (a) vertical ground reaction forces decreased during early stance and increased during mid-stance, (b) decreased knee excursion, (c) increased internal extension moment throughout stance, and (d) decreased internal knee abduction moment peaks. Cueing a 5% body weight increase in vertical ground reaction force impact peak resulted in a more dynamic vertical ground reaction force loading pattern, increased knee excursion, and a greater internal extension moment during stance which may be useful in restoring gait patterns following anterior cruciate ligament reconstruction. • Vertical ground reaction force impact peak can be modified with real-time feedback. • A single cue can be used to modify multiple gait biomechanics throughout stance. • Cueing a higher impact peak leads to greater knee flexion excursion during stance. • Cueing a higher impact peak leads to increased internal knee extension moment. • Cueing a lower impact peak leads to a stiffened knee gait strategy. [ABSTRACT FROM AUTHOR]