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Objective: To determine whether (i) low back loads and/or (ii) kinematic coordination patterns differed across theoretical expert, contextual expert and novice groups when completing both generic and occupation-specific lifts. Background: Experience has been proposed as a factor that could reduce biomechanical exposures in lifting, but the literature reports mixed effects. The inconsistent relationship between experience and exposures may be partially attributable to the broad classification of experience and experimental lifting protocols not replicating the environment where experience was gained. Methods: Purposive sampling was used to recruit 72 participants including theoretical experts (formal training on lifting mechanics), contextual experts (paramedics), and novices. Participants performed 10 barbell and crate (generic) lifts, as well as backboard and stretcher (occupation-specific) lifts while whole-body kinematics and ground reaction forces were collected. Peak low back compression and anteroposterior shear loads normalized to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. Results: No significant differences in low back loads were observed across expertise groups. However, significant differences were seen in kinematic coordination patterns across expertise groups in occupation-specific lifts, but not in generic lifts. Conclusion: Increasing expertise is unlikely to minimize low back loads in lifting. However, contextual expertise did influence lifting kinematics, but only when performing occupationally specific lifts. Application: Contextual expertise may help lifters adopt lifting kinematics that enhance the tolerance of their musculoskeletal system to withstand applied loads, but does not seem to reduce the applied low back loads relative to noncontextual expert groups. [ABSTRACT FROM AUTHOR]

This study evaluated whether real-time applied load feedback and a predefined applied load limit improved inter-session reliability and measurement error of passive glenohumeral rotation range-of-motion measurements. Twenty-one male recreational overhead athletes completed two data collection sessions, approximately 1-week apart. Measurements of internal and external rotation range-of-motion and clinician-applied loads were obtained and side-to-side differences were calculated. A load limit of 4 Nm was used for feedback trials. Perception of a capsular end-feel was used for no-feedback trials. Intraclass correlation coefficients (ICCs), standard errors of measurement (SEMs) and minimal detectable changes (MDCs) were derived. ICCs from single trials with and without feedback ranged from 0.72-0.93 and 0.63-0.89, respectively. SEMs ranged from 2.6°-6.1° with feedback and 3.3°-6.0° without feedback. MDCs from single trials with and without feedback ranged from 7.2°-16.8° and 9.1°-16.7°, respectively. Applied load feedback did not improve, already moderate to excellent, inter-session reliability and SEM for passive glenohumeral rotation range-of-motion measurements.

There is disagreement regarding the efficacy of 'safe' lifting recommendations for reducing low back disorder risk. These recommendations commonly focus on minimising lumbar spine flexion, which limits the range of allowable starting lift positions for that person. This study evaluated whether starting postural adaptations could allow a person to reach down further without rounding their lumbar spine before beginning a lift. Reach displacement was measured as participants performed a series of maximal reach tasks under different combinations of stance width, foot orientation and trunk inclination, with their lumbar spine motion restricted. There were no interactions between any of the three postural adaptations or any effect of stance width or trunk inclination. Seventy-nine percent of participants achieved their greatest reach displacement with their feet externally rotated, which contributed to a 4 cm greater reach displacement compared to a neutral foot orientation (p < 0.001). Practitioner summary: This study examined whether aspects of initial posture could influence the ability to adhere to 'safe' lifting recommendations across a range of lift heights. As a component of lifting (re)training interventions, practitioners should consider starting lift posture adaptations (e.g. manipulating foot external rotation) to improve capacity to adhere to recommendations. [ABSTRACT FROM AUTHOR]

It is unknown how structural (sex, stature, body mass) and functional (strength, flexibility) personal factors influence lifting strategy in paramedic work. We explored whether variance in peak low back forces and kinematic coordination patterns could be explained by structural and functional personal factors in paramedic lifting tasks. Seventy-two participants performed backboard and stretcher lifts. Peak low back forces normalised to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. Being female, stronger, shorter, having higher body mass, and/or having greater lower body range of motion (ROM) were all independently associated with lower normalised low back forces across backboard and stretcher lifting. Females and stronger individuals seemed to define a movement objective to consistently minimise compressive forces, while individuals with greater hip ROM consistently minimised anteroposterior shear forces. The efficacy of improving strength and hip ROM to reduce low back forces in paramedic lifting should be investigated. Practitioner summary: Females, stronger individuals, and individuals with greater hip range of motion consistently exhibited lower normalised low back forces in paramedic lifting. Improving strength and hip range of motion via training is a potential proactive ergonomics approach to reduce peak low back forces in paramedic lifting tasks. [ABSTRACT FROM AUTHOR]

The scoring scheme for the functional movement screen implicitly assumes that the factor structure is consistent, stable, and congruent across different populations. To determine if this is the case, we compared principal components analyses of three samples: a healthy, general population (n = 100), a group of varsity athletes (n = 101), and a group of firefighters (n = 397). The congruence of the principal components derived through these analyses were evaluated across all of the samples, using Tucker's congruence coefficient. Factor extraction was guided by parallel analyses, and interpretation was facilitated by Varimax rotation. We observed factor instability, low factor congruence, and inconsistent factor structure. Additionally, we observed a two-factor structure of the functional movement screen in all of our sample groups. These analyses suggest that, although the independent elements of the functional movement screen may continue to be used, use of the composite score is not supported by the factor structure of the measure.

Ratio scaling is the most common magnitude normalization approach for net joint moment (NJM) data. Generally, researchers compute a ratio between NJM and (some combination of) physical body characteristics (eg. mass, height, limb length, etc). However, 3 assumptions must be verified when normalizing NJM data this way. First, the regression line between NJM and the characteristic(s) used passes through the origin. Second, normalizing NJM eliminates its correlation with the characteristic(s). Third, the statistical interpretations following normalization are consistent with adjusted linear models. The study purpose was to assess these assumptions using data collected from 16 males and 16 females who performed a single-leg squat. Standard inverse dynamics analyses were conducted, and ratios were computed between the mediolateral and anteroposterior components of the knee NJM and participant mass, height, leg length, mass x height, and mass x leg length. Normalizing NJM-mediolateral by mass x height and mass x leg length satisfied all 3 assumptions. Normalizing NJM-anteroposterior by height and leg length satisfied all 3 assumptions. Therefore, if normalization of the knee NJM is deemed necessary to address a given research question, it can neither be assumed that using (any combination of) participant mass, height, or leg length as the denominator is appropriate nor consistent across joint axes. [ABSTRACT FROM AUTHOR]

Background Few studies have quantified dynamic balance in fencers despite previous suggestions that balance training may be beneficial for these athletes. Generally, asymmetry in dynamic balance performance between the left and right legs can be an indicator of lower extremity injury risk and used to monitor rehabilitation progress. Fencing is recognized as an asymmetric sport, therefore, differences in dynamic balance may exist among uninjured athletes. Hypothesis/Purpose The primary objective of this investigation was to evaluate whether asymmetry of dynamic balance is present in uninjured national-level fencers. It was hypothesized that elite uninjured fencers would demonstrate superior dynamic balance on the lead-leg of their fencing stance. A secondary objective was to compare dynamic balance performance of elite fencers to previously published data from high-level athletes participating in other sports. Study Design Descriptive Laboratory Study Methods Fourteen uninjured elite competitive fencers were recruited. Subjects self-reported the lead leg of their fencing stance. Each participant performed the Y-Balance test (YBT), which represented a measurement of dynamic balance control, on both legs. Reach distances were recorded directly from a commercially available YBT apparatus. Four reach distances were recorded: anterior, posteromedial, posterolateral, and a composite measure was calculated. Distances were leg length-normalized and expressed as a percentage. Sample averages and standard deviations were derived for the four YBT measurements. Results There were no significant differences in reaching distance between the lead and trail legs in any of the four YBT measures (p ≥ 0.65). Fencers appeared to demonstrate larger normalized reach distances in the posterolateral and posteromedial directions than other athletes. Conclusions The results of this study indicate that dynamic balance is not significantly different between the lead and trail legs in elite fencers, despite the asymmetrical nature of their sport. The apparent symmetry of dynamic balance control in uninjured fencers means that the YBT could be used in this population for monitoring progress during training and rehabilitation. Level of Evidence 2b [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate why holding times on 2 different tests of isometric trunk flexor endurance capacity (prone plank and v-sit) are weakly correlated. Body position and ground reaction force data from 10 men and 10 women were used to conduct static biomechanical analyses of both test postures, and bilateral activations of the rectus abdominis, internal and external obliques, latissimus dorsi, and lumbar and thoracic erector spinae were measured in a second sample of 15 men and 15 women while holding the test postures. No between-posture differences in net low back flexor moments were found (P = .111), but the lumbar spine was 28° more flexed in the v-sit than in the plank (P < .001). No between-posture differences were detected in the rectus abdominis (P = .397), external obliques (P = .204), internal obliques (P = .226), or lumbar erector spinae (P = .116) activation levels, but those of the thoracic erector spinae (P = .0253) and latissimus dorsi (P < .001) were greater in the plank than in the v-sit. Altogether, the findings suggest that differences between plank and v-sit holding times are most likely related to between-test differences in lumbar spine postures and shoulder demands. [ABSTRACT FROM AUTHOR]

Inter-segmental coordination patterns and mechanical energy transfer were compared between vertical jumping tasks which possess different countermovement characteristics. Thirteen participants completed squat (SJ), countermovement (CMJ) and drop (DVJ) vertical jumps. Inter-segmental coordination patterns became more out-of-phase with increases in countermovement velocity (DVJ > CMJ > SJ), at the ankle, hip and lumbar spine (all p < 0.05), but not at the knee. With countermovements, more inter-segmental energy transfer occurred at all joints (p < 0.05), but increasing the countermovement velocity (DVJ compared to CMJ) did not always increase energy transfer (p < 0.001 for the hip and knee, p > 0.05 for the ankle and lumbar spine). The relationship between mechanical energy transfer and inter-segmental coordination patterns during vertical jumping is not straightforward since the responses to these varying countermovement demands were not consistent across all joints. [ABSTRACT FROM AUTHOR]

Purpose. To compare the effects of object handled and handgrip used on lumbar spine motion and loading during occupational lifting task simulations. Methods. Eight male and eight female volunteers performed barbell and crate lifts with a pronated (barbell) and a neutral (crate) handgrip. The mass of barbells/crates lifted was identical across the objects and fixed at 11.6 and 9.3 kg for men and women, respectively. The initial heights of barbells/crates were individualized to mid-shank level. Body segment kinematics and foot–ground reaction kinetics were collected, and then input into an electromyography-assisted dynamic biomechanical model to quantify lumbar spine motion and loading. Results. Lumbar compression and net lumbosacral moment magnitudes were 416 N and 17 Nm lower when lifting a barbell than when lifting a crate (p < 0.001), respectively. There were no between-condition differences in lumbar flexion displacements (p > 0.392) or flexion/extension velocities (p > 0.085). Conclusions. Crate- and barbell-lifting tasks can be used interchangeably if assessing lifting mechanics based on peak spine motion variables. If assessments are based on the spine loading responses to task demands, however, then crate- and barbell-lifting tasks cannot be used interchangeably. [ABSTRACT FROM AUTHOR]

Background: The side-bridge (SB) is a commonly used closed-chain task to assess trunk muscle endurance and side-to-side endurance asymmetry. An open-chain variation of the SB, that positions the participant in an inclined side-lying posture, may be useful for those who report shoulder pain or fatigue as the reason for terminating the closed-chain SB. Low back loading demands of the open- and closed-chain variations should be matched to facilitate comparison of SB endurance measures. Purpose: To quantify the low back reaction moments during the open- and closed-chain SB and determine the appropriate open-chain angle of inclination that matches the lateral bend moment magnitude of the closed-chain SB. Study Design: Observational cohort Methods: Upper body and trunk postural data were obtained during the closed-chain SB and during the open-chain SB at each of four inclination angles from a group of eight healthy male adults. Ground reaction force (GRF) data were also collected during the closed-chain SB. Low back reaction moments were calculated using a static 'top-down' linked segment model in both SB variations. Latent growth modeling was used to determine the angle of inclination in the open-chain SB that produced a low back lateral bend moment that matched the closed-chain SB. Sensitivity of the matching open-chain inclination angle was evaluated by rotating the measured GRF vector from the closed-chain SB by five degrees clockwise and counter-clockwise in the frontal plane. Results: The open-chain inclination angle that best matched the loading demands of the closed-chain SB was 38±12 degrees. Clockwise rotation of the measured GRF in the closed-chain SB increased the matching inclination angle to 56±17 degrees. Counter-clockwise rotation reduced the matching inclination angle to 17±11 degrees. Secondary descriptive analysis of spine posture and off-axis low back moments revealed biomechanically relevant differences between SB positions. Conclusion: The average open-chain SB angle of inclination that matched the closed-chain SB approximated the 45-degree recommendation offered in the literature. Differences in spine posture and off-axis low back reaction moments, and the potential impact on holding times, should be considered if using the open-chain SB. [ABSTRACT FROM AUTHOR]

The goal of this study was to quantify the relative contributions of each muscle group surrounding the spine to vertebral joint rotational stiffness (VJRS) during the push-up exercise. Upper-body kinematics, three-dimensional hand forces and lumbar spine postures, and 14 channels (bilaterally from rectus abdominis, external oblique, internal oblique, latissimus dorsi, thoracic erector spinae, lumbar erector spinae, and multifidus) of trunk electromyographic (EMG) activity were collected from 11 males and used as inputs to a biomechanical model that determined the individual contributions of 10 muscle groups surrounding the lumbar spine to VJRS at five lumbar vertebral joints (L1-L2 to L5-S1). On average, the abdominal muscles contributed 64.32 ± 8.50%, 86.55 ± 1.13%, and 83.84 ± 1.95% to VJRS about the flexion/extension, lateral bend, and axial twist axes, respectively. Rectus abdominis contributed 43.16 ± 3.44% to VJRS about the flexion/extension axis at each lumbar joint, and external oblique and internal oblique, respectively contributed 52.61 ± 7.73% and 62.13 ± 8.71% to VJRS about the lateral bend and axial twist axes, respectively, at all lumbar joints with the exception of L5-S1. Owing to changes in moment arm length, the external oblique and internal oblique, respectively contributed 55.89% and 50.01% to VJRS about the axial twist and lateral bend axes at L5-S1. Transversus abdominis, multifidus, and the spine extensors contributed minimally to VJRS during the push-up exercise. The push-up challenges the abdominal musculature to maintain VJRS. The orientation of the abdominal muscles suggests that each muscle primarily controls the rotational stiffness about a single axis. [ABSTRACT FROM AUTHOR]

Khuu, S, Musalem, LL, and Beach, TAC. Verbal instructions acutely affect drop vertical jump biomechanics—Implications for athletic performance and injury risk assessments. J Strength Cond Res 29(10): 2816-2826, 2015—Biomechanical quantities acquired during the drop vertical jump (DVJ) are used in the assessment of athletic performance and injury risk. The objective was to examine the impact of different verbal instructions on spatiotemporal, kinematic, and kinetic variables commonly included in such assessments. Ten men and 10 women from local varsity and club volleyball, basketball, figure skating, and track and field teams volunteered to participate. The athletes performed DVJs after given instructions to minimize ground contact time (CT), maximize jump height (HT), and synchronously extend the lower extremity joints (EX). Between the CT, HT, and EX conditions, body segment and joint angles were compared together with characteristics of vertical ground reaction force (GRF), whole-body power output, stiffness, and center-of-mass displacement time histories. Verbal instructions were found to influence nearly all of the spatiotemporal, body segment and joint kinematic, and kinetic variables that were statistically analyzed. Particularly noteworthy was the finding that athletic performance indices (e.g., jump height, power output, vertical stiffness, and reactive strength index) and lower extremity injury risk markers (e.g., peak vertical GRF and frontal plane knee angle) were significantly different (p # 0.05) between the CT, HT, and EX conditions. The findings of this study suggest that verbal instructions should be controlled and/ or clearly documented when using the DVJ to assess athletic performance potential and injury risk. Moreover, practitioners who devise performance enhancement and injury prevention strategies based on DVJ assessments are advised to consider that “coaching” or “cueing” during the task execution could impact conclusions drawn. [ABSTRACT FROM AUTHOR]

BACKGROUND: Within the context of evaluating individuals' movement behavior it is generally assumed that the tasks chosen will predict their competency to perform activities relevant to their occupation. OBJECTIVE: This study sought to examine whether a battery of general tasks could be used to predict the movement patterns employed by firefighters to perform select job-specific skills. METHODS: Fifty-two firefighters performed a battery of general and occupation-specific tasks that simulated the demands of firefighting. Participants' peak lumbar spine and frontal plane knee motion were compared across tasks. RESULTS: During 85% of all comparisons, the magnitude of spine and knee motion was greater during the general movement tasks than observed during the firefighting skills. Certain features of a worker's movement behavior may be exhibited across a range of tasks. Therefore, provided that a movement screen's tasks expose the motions of relevance for the population being tested, general evaluations could offer valuable insight into workers' movement competency or facilitate an opportunity to establish an evidence-informed intervention. [ABSTRACT FROM AUTHOR]

Estimates of cumulative load are typically based on a direct integration of instantaneous compressive loads. Recent evidence suggests that higher loads as well as smaller rest to work durations should receive greater importance in the calculation of cumulative compressive load, especially if insight into potential injury mechanisms is sought. The purpose of this investigation was to determine the effects that a novel weighting factor protocol would have on cumulative compressive load estimates using three different biomechanical models applied to a repetitive lifting task. Bilateral electromyographic activity of the external abdominal obliques and lumbar erector spinae, as well as unilateral kinematics of the upper body were collected from eight male and eight female participants while they performed a 5-min repetitive lifting/lowering task at a rate of one lift/lower every 6 seconds. Two-dimensional reaction L5/S1 joint kinetics were calculated using each of a static, quasi-static and dynamic linked segment model; muscular contributions to L5/S1 compression were computed using a single equivalent muscle model. Unweighted and weighted cumulative compression was calculated for each model type. Application of the weighting factor increased the estimates of cumulative compression for both the male and female participants. Since the males in this study loaded their spines to a relatively higher percentage of their predicted compressive strength when lifting/lowering, the effects of weighting instantaneous compressive loads had a greater influence on cumulative load magnitudes in males. A consistent finding between genders was that estimates of cumulative compressive joint loads from the dynamic model were most affected by applying weighting factors, as the inclusion of inertial information in the calculations lead to greater predicted compressive forces relative to estimated compressive strength. These findings suggest that biomechanical modelling assumptions made and the gender of the participants tested could influence interpretations drawn from studies using force-weighting approaches to understand potential injury mechanisms associated with cumulative exposures. Future work is needed to explore more thoroughly the influence of different rest to work durations on weighted cumulative load estimates. [ABSTRACT FROM AUTHOR]

When lifting an object from the ground a person has many possible whole-body movement solutions to accomplish the task. It is unclear why lifters use most of their available lumbar spine flexion range-of-motion despite many ergonomic guidelines advising against doing so. Experimentally restricting spine motion and observing compensatory movement strategies is one approach to address this knowledge gap. A kinematic analysis was performed on 16 participants who completed symmetrical lifting tasks with and without wearing a spine motion-restricting device. Sagittal trunk, lumbar spine, and lower extremity kinematics, along with stance width and foot orientation in the transverse plane were evaluated between restricted and unrestricted lifting conditions. Restricting spine motion required greater ankle dorsiflexion (p < 0.001), knee flexion (p < 0.001), and hip flexion (p < 0.001) motion in comparison to unrestricted lifting. Motion was reallocated such that hip flexion showed the largest increase in restricted lifting, followed by ankle dorsiflexion, then knee flexion compared to unrestricted lifting. Trunk inclination decreased (i.e., more upright) in restricted compared to unrestricted lifting (p < 0.001). Neither stance width (p = 0.163) nor foot orientation (p = 0.228) were affected by restricting spine motion. These adaptive movements observed indicate lower extremity joint motion must be available and controlled to minimize lumbar spine flexion during lifting., 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.)

Abstract: Hirsch, SM, Chapman, CJ, Frost, DM, and Beach, TAC. Mechanical energy expenditure at lumbar spine and lower extremity joints during the single-leg squat is affected by the nonstance foot position. J Strength Cond Res 36(9): 2417-2426, 2022-Previous research has shown that discrete kinematic and kinetic quantities during bodyweight single-leg squat (SLS) movements are affected by elevated foot positioning and sex of the performer, but generalizations are limited by the high-dimensional data structure reported. Using a 3D inverse dynamical linked-segment model, we quantified mechanical energy expenditure (MEE) at each joint in the kinetic chain, the total MEE (sum of MEE across aforesaid joints), and the relative contribution of each joint to total MEE during SLSs performed with elevated foot positioned beside stance leg (SLS-Side), and in-front of (SLS-Front) and behind (SLS-Back) the body. Total MEE differed between SLS variations ( p = 0.002), with the least amount observed in the SLS-Back (effect size [ES] = 0.066-0.069). Approximately 50% of total MEE was contributed by the knee joint in each SLS variation, whereas MEE at the ankle, hip, and lumbar spine (in absolute and relative terms) varied complexly as a function of the elevated foot position. Total MEE ( p = 0.0192, ES = 0.852) and the absolute MEE at the knee and spine was greater in men across the SLS variations performed ( p = 0.025-0.036, ES = 0.715-0.766), but only the lumbar spine contribution to total MEE was larger in men across all SLS variations ( p = 0.045, ES = 0.607). Otherwise, there were no other sex-specific responses observed. Biomechanically, SLS movements are generally "knee-dominant," but changing elevated foot position effectively redistributes MEE among other joints in the linkage. Consistent with the previous conclusions reached based on discrete kinematic and kinetic data, not all SLSs are equal., (Copyright © 2020 National Strength and Conditioning Association.)

Little is known about the construct validity of the Functional Movement Screen (FMS). We aimed to assess associations between FMS task scores and measures of maximum joint range-of-motion (ROM) among university varsity student-athletes from 4 sports (volleyball, basketball, ice hockey, and soccer). Athletes performed FMS tasks and had their maximum ankle, hip and shoulder ROM measured. Multivariable linear regression was used to estimate associations between FMS task scores and ROM measurements. 101 university student-athletes were recruited (52 W/49 M; mean age 20.4±1.9 years). In general, athletes with higher FMS task scores had greater ROM compared to those with lower task scores. For example, athletes who scored 2 on the FMS squat task had 4° (95% CI, 1° to 7°) more uni-articular ankle dorsiflexion ROM compared with those who scored 1, while those who scored 3 on the FMS squat task had 10° (4° to 17°) more uni-articular ankle dorsiflexion ROM compared with those who scored 1. Large variation in ROM measurements was observed. In sum, substantial overlap in joint ROM between groups of athletes with different FMS task scores weakens the construct validity of the FMS as an indicator of specific joint ROM., Competing Interests: The authors declare that they have no conflict of interest, (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

Manual handling training may be improved if it relied on the provision of individualized, augmented feedback about key movement features. The purpose of this study was to compare the reduction in sagittal spine motion during manual lifting tasks following two training approaches: didactic (DID) and augmented feedback (AUG). Untrained participants (n = 26) completed lifting tests (box, medication bag, and paramedic backboard) and a randomly-assigned intervention involving 50 practice box lifts. Lifting tests were performed immediately before and after training, and one-week after interventions. Both groups exhibited reductions in spine motions immediately and one-week after the interventions. However, the AUG intervention group elicited significantly greater reductions in 5 of 12 between-group comparisons (3 tasks × 4 spine motion variables). The results of the current study support the use of augmented feedback-based approaches to manual handling training over education-based approaches., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The relationship between internal loading dose and low-back injury risk during lifting is well known. However, the implications of movement parameters that influence joint loading rates-movement frequency and speed-on time-dependent spine loading responses remain less documented. This study quantified the effect of loading rate and frequency on the tolerated cumulative loading dose and its relation to joint lifespan. Thirty-two porcine spinal units were exposed to biofidelic compression loading paradigms that differed by joint compression rate (4.2 and 8.3 kN/s) and frequency (30 and 60 cycles per minute). Cyclic compression testing was applied until failure was detected or 10,800 continuous cycles were tolerated. Instantaneous weighting factors were calculated to evaluate the cumulative load and Kaplan-Meier survival probability functions were examined following nonlinear dose normalization of the cyclic lifespan. Significant reductions in cumulative compression were tolerated when spinal units were compressed at 8.3 kN/s (P < .001, 67%) and when loaded at 30 cycles per minute (P = .008, 45%). There was a positive moderate relationship between cumulative load tolerance and normalized cyclic lifespan (R2 = .52), which was supported by joint survivorship functions. The frequency and speed of movement execution should be evaluated in parallel to loading dose for the management of low-back training exposures.

Purpose. This study aimed to determine whether untrained observers alter their spine as directed via static images of different lifting techniques. Methods. Ten men and eight women, who had no lifting or visual observation training, performed box lifts. Following a self-selected lifting technique trial, participants performed four experimental lifting trials (in randomized order) wherein they were instructed to execute lifts in accordance with the techniques pictured. These techniques differed by the amount of knee, trunk and spine flexion modeled. Peak lumbar flexion angles and flexion/extension velocities were quantified, and then statistically analyzed via general linear models with two within-participant factors (condition = technique; phase = lift/lower). Results . Lumbar flexion angles and flexion/extension velocities differed between conditions ( p  < 0.001), although the effects depended on the combination of postural characteristics pictured. A main effect of phase was observed for peak lumbar flexion velocity only ( p  = 0.001). No condition × phase interaction effects were detected for any dependent variables ( p  > 0.050). Conclusions. Acute changes in lifting mechanics can be elicited via visual observation of pictured techniques. However, if using pictures to attenuate peak lumbar flexion displacements and velocities when lifting, auxiliary instruction may be needed to direct observers' attention to the spine curvature displayed.

The Turkish Get-Up (TGU) is a complex and multi-planar exercise; the performer begins in a supine lying position, progresses toward upright standing through a series of 7 stages while holding a mass overhead in one hand, and returns to the original supine lying position through a reversal of the same 7 stages. A descriptive analysis of shoulder muscle activity during the TGU may provide insight toward its use in training and rehabilitation contexts. Our objectives were to: (1) describe the activity patterns from a subset of muscles that span the glenohumeral joint during individual stages of the TGU, and (2) interpret these patterns through comparisons between left- and right-side muscles, and between the up and down phases of the TGU. Twelve individuals with at least one-year experience performing the TGU were included in this study. Surface electromyographic (EMG) recordings were bilaterally obtained from 8 glenohumeral muscle groups while participants performed ten trials of the TGU with a kettlebell in their right hand. Instants representing the start and end of each TGU stage were identified from a synchronized video for each trial, and EMG activities for each muscle were integrated over the duration of each stage. Average integrated EMG and within-participant coefficients of variation were calculated. Overall, the greatest muscular demand occurred during the second (press to elbow support) and fifth (leg sweep) stages. Activities from muscles on the ipsilateral side to the kettlebell (right-side) were greater during stages when the contralateral upper limb did not contribute to supporting the body; however, contralateral (left-side) muscles were invoked during stages when the non-kettlebell-bearing forearm or hand contributed to supporting the body. The results suggest the importance of training both phases of the TGU to gain the most benefit from the exercise and highlights the asymmetric nature of the exercise, which may be particularly relevant for athletes engaged in activities with rotational demands., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Estimation of muscle forces through musculoskeletal simulation is important in understanding human movement and injury. Unmatched filter frequencies used to low-pass filter marker and force platform data can create artifacts during inverse dynamics analysis, but their effects on muscle force calculations are unknown. The objective of this study was to determine the effects of filter cutoff frequency on simulation parameters and magnitudes of lower-extremity muscle and resultant joint contact forces during a high-impact maneuver. Eight participants performed a single-leg jump landing. Kinematics was captured with a 3D motion capture system, and ground reaction forces were recorded with a force platform. The marker and force platform data were filtered using 2 matched filter frequencies (10-10 Hz and 15-15 Hz) and 2 unmatched filter frequencies (10-50 Hz and 15-50 Hz). Musculoskeletal simulations using computed muscle control were performed in OpenSim. The results revealed significantly higher peak quadriceps (13%), hamstrings (48%), and gastrocnemius forces (69%) in the unmatched (10-50 Hz and 15-50 Hz) conditions than in the matched (10-10 Hz and 15-15 Hz) conditions (P < .05). Resultant joint contact forces and reserve (nonphysiologic) moments were similarly larger in the unmatched filter categories (P < .05). This study demonstrated that artifacts created from filtering with unmatched filter cutoffs result in altered muscle forces and dynamics that are not physiologic.

Low-back disorder risk can be modulated by pelvis-thorax coordination when lifting. To objectively discriminate between coordination patterns during lifting, the analytical methods used require evaluation. The primary study objective was to determine if continuous relative phase (CRP) and vector coding (VC) analyses can discriminate between lifting techniques that differ based on biomechanical risk criteria. The secondary objective was to determine if normalization/transformation of input segmental angular position and velocity data is required to discriminate between lifting techniques. Sixteen volunteers performed a sagittal lifting task using freestyle (FRE), flexed spine (FLX), and neutral spine (NTL) techniques. CRP and VC analyses were implemented to quantify pelvis-thorax coordination patterns based on time-normalized, phase-normalized, and Hilbert-transformed segmental angular kinematic data. Mean relative phase angles along with thorax-only and in-phase coupling patterns were significantly different between FRE-NTL and FLX-NTL techniques (p < 0.01), but not FRE-FLX (p > 0.44). This finding was consistent across all relative phase normalization/transformation methods. Therefore, CRP and VC analyses successfully discriminated between different lifting techniques, regardless of the relative phase normalization/transformation method used., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This investigation examined interactions between the magnitude of external load, movement speed and (a)symmetry of load placement on estimates of in vivo joint loading in the lumbar spine during simulated occupational lifting. Thirty-two participants with manual materials handling experience were included in the study. Three-dimensional motion data, ground reaction forces, and activation of six bilateral trunk muscle groups were captured while participants performed lifts with two loads at two movement speeds and using two load locations. L4-L5 joint compression and shear force-time histories were estimated using an EMG-assisted musculoskeletal model of the lumbar spine. Results from this investigation provide strong evidence that known mechanical low back injury risk factors should not be viewed in isolation. Rather, injury prevention efforts need to consider the complex interactions that exist between external task demands and their combined influence on internal joint loading., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

"Use your legs" is commonly perceived as sound advice to prevent lifting-related low-back pain and injuries, but there is limited evidence that this directive attenuates the concomitant biomechanical risk factors. Body segment kinematic data were collected from 12 men and 12 women who performed a laboratory lifting/lowering task after being provided with different verbal instructions. The main finding was that instructing participants to lift "without rounding your lower back" had a greater effect on the amount of spine flexion they exhibited when lifting/lowering than instructing them to lift "with your legs instead of your back" and "bend your knees and hips". It was concluded that if using verbal instructions to discourage spine flexion when lifting, the instructions should be spine- rather than leg-focused., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Objective: To examine whether objective measures of spine and frontal plane knee motion exhibited during Functional Movement Screen™ (FMS) task performance changed following a movement-guided fitness (MOV) and conventional fitness (FIT) exercise intervention., Design: Secondary analysis of a randomized controlled experiment. Before and after 12 weeks of exercise, participants' kinematics were quantified while performing the FMS and a series of general whole-body movement tasks., Setting: Biomechanics laboratory., Participants: Fifty-two firefighters were assigned to MOV, FIT, or a control (CON) group., Outcome Measures: Peak lumbar spine flexion/extension, lateral bend and axial twist, and frontal plane knee motion., Results: The post-training kinematic changes exhibited by trainees while performing the FMS tasks were similar in magnitude (effect size < 0.8) to those exhibited by CON. However, when performing the battery of general whole-body movement tasks, only MOV showed significant improvements in spine and frontal plane knee motion control (effect size > 0.5)., Conclusions: Whether graded qualitatively, or quantitatively via kinematic analyses, the FMS may not be a viable tool to detect movement-based exercise adaptations. Amendments to the FMS tasks and/or scoring method are needed before it can be used for reasons beyond appraising the ability to move freely, symmetrically, and without pain., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Altering footwear worn during performance of the barbell back squat has been shown to change motion patterns, but it is not completely understood how this affects biomechanical loading demands. The primary objective was to compare lower back and extremity net joint moments in 24 experienced weightlifters (12M, 12F) who performed 80% one-repetition maximum back squats under three different footwear conditions (barefoot, running shoes, weightlifting shoes). Results showed that there was a significant main effect of footwear condition on the knee extension moment (p=0.001), where the running and weightlifting shoes produced significantly larger moments than the barefoot condition. There was also a main effect of footwear condition on knee external rotation moments (p=0.002), where the weightlifting shoe produced significantly larger moments than both other conditions. At the hip, there was also a main effect of footwear condition on the extension moment (p=0.004), where the barefoot condition produced significantly larger moments than either the running shoe or weightlifting shoe condition. Lastly, there was also a significant main effect of footwear condition on both hip external (p=0.005) and internal (p=0.003) rotation moments, where the barefoot condition produced greater internal rotation and less external rotation moments than either shod condition. This study indicates that altering footwear conditions while performing the barbell back squat may redistribute the internal biomechanical loading patterns amongst the lower extremity joints and perhaps alter the musculoskeletal adaptations elicited., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Deficits in joint mobility and stability could certainly impact individuals' Functional Movement Screen (FMS) scores; however, it is also plausible that the movement patterns observed are influenced by the performers' knowledge of the grading criteria. Twenty-one firefighters volunteered to participate, and their FMS scores were graded before and immediately after receiving knowledge of the movement patterns required to achieve a perfect score on the FMS. Standardized verbal instructions were used to administer both screens, and the participants were not provided with any coaching or feedback. Time-synchronized sagittal and frontal plane videos were used to grade the FMS. The firefighters significantly (p < 0.001) improved their FMS scores from 14.1 (1.8) to 16.7 (1.9) when provided with knowledge pertaining to the specific grading criteria. Significant improvements (p < 0.05) were also noted in the deep squat (1.4 [0.7]-2.0 [0.6]), hurdle step (2.1 [0.4]-2.4 [0.5]), in-line lunge (2.1 [0.4]-2.7 [0.5]), and shoulder mobility (1.8 [0.8]-2.4 [0.7]) tests. Because a knowledge of a task's grading criteria can alter a general whole-body movement screen score, FMS or otherwise, observed changes may not solely reflect "dysfunction." The instant that individuals are provided with coaching and feedback regarding their performance on a particular task, the task may lose its utility to evaluate the transfer of training or predict musculoskeletal injury risk.

Objective: To examine the relationship between the composite Functional Movement Screen (FMS) score and performers' spine and frontal plane knee motion., Design: Examined the spine and frontal plane knee motion exhibited by performers who received high (>14) and low (<14) composite FMS scores. Participants' body motions were quantified while they performed the FMS., Setting: Biomechanics laboratory., Participants: Twelve men who received composite FMS scores greater than 14 were assigned to a high-scoring group. Twelve age-, height- and weight-matched men with FMS scores below 14 were assigned to a low-scoring group., Outcome Measures: Composite FMS scores and peak lumbar spine flexion/extension, lateral bend and axial twist, and left and right frontal plane knee motion., Results: Significant differences (p < 0.05) and large effect sizes (>0.8) were noted between the high- and low-scoring groups when performing the FMS tasks; high-scorers employed less spine and frontal plane knee motion. Substantial variation was also observed amongst participants., Conclusions: Participants with high composite FMS scores exhibited less spine and frontal plane knee motion while performing the FMS in comparison to their low-scoring counterparts. However, because substantial variation was observed amongst performers, the FMS may not provide the specificity needed for individualized injury risk assessment and exercise prescription., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Because individuals' movement patterns have been linked to their risk of future injury, movement evaluations have become a topic of interest. However, if individuals adapt their movement behavior in response to the demands of a task, the utility of evaluations comprising only low-demand activities could have limited application with regard to the prediction of future injury. This investigation examined the impact of load and speed on individuals' movement behavior. Fifty-two firefighters performed 5 low-demand (i.e., light load, low movement speed) whole-body tasks (i.e., lift, squat, lunge, push, and pull). Each task was then modified by increasing the speed, external load, or speed and load. Select measures of motion were used to characterize the performance of each task, and comparisons were made between conditions. The participants adapted their movement behavior in response to the external demands of a task (64 and 70% of all the variables were influenced [p ≤ 0.05] by changing the load and speed, respectively), but in a manner unique to the task and type of demand. The participants exhibited greater spine and frontal plane knee motion in response to an increase in speed when compared with increasing loads. However, there were a large number of movement strategies exhibited by individual firefighters that differed from the group's response. The data obtained here imply that individuals may not be physically prepared to perform safely or effectively when a task's demands are elevated simply because they exhibit the ability to perform a low-demand activity with competence. Therefore, movement screens comprising only low-demand activities may not adequately reflect an individual's capacity, or their risk of injury, and could adversely affect any recommendations that are made for training or job performance.

Using exercise to enhance physical fitness may have little impact on performers' movement patterns beyond the gym environment. This study examined the fitness and movement adaptations exhibited by firefighters in response to 2 training methodologies. Fifty-two firefighters were assigned to a movement-guided fitness (MOV), conventional fitness (FIT), or control (CON) group. Before and after 12 weeks of training, participants performed a fitness evaluation and laboratory-based test. Three-dimensional lumbar spine and frontal plane knee kinematics were quantified. Five whole-body tasks not included in the interventions were used to evaluate the transfer of training. FIT and MOV groups exhibited significant improvements in all aspects of fitness; however, only MOV exhibited improvements in spine and frontal plane knee motion control when performing each transfer task (effect sizes [ESs] of 0.2-1.5). FIT exhibited less controlled spine and frontal plane knee motions while squatting, lunging, pushing, and pulling (ES: 0.2-0.7). More MOV participants (43%) exhibited only positive posttraining changes (i.e., improved control), in comparison with FIT (30%) and CON (23%). Fewer negative posttraining changes were also noted (19, 25, and 36% for MOV, FIT, and CON). These findings suggest that placing an emphasis on how participants move while exercising may be an effective training strategy to elicit behavioral changes beyond the gym environment. For occupational athletes such as firefighters, soldiers, and police officers, this implies that exercise programs designed with a movement-oriented approach to periodization could have a direct impact on their safety and effectiveness by engraining desirable movement patterns that transfer to occupational tasks.

The primary objective was to examine the utility of a novel method of detecting "actual" kinematic changes using the within-subject variation. Twenty firefighters were assigned to one of two groups (lifting or firefighting). Participants performed 25 repetitions of two lifting or firefighting tasks, in three sessions. The magnitude and within-subject variation of several discrete kinematic measures were computed. Sequential averages of each variable were used to derive a cubic, quadratic and linear regression equation. The efficacy of each equation was examined by contrasting participants' sequential means to their 25-trial mean±1SD and 2SD. The magnitude and within-subject variation of each dependent measure was repeatable for all tasks; however, each participant did not exhibit the same movement patterns as the group. The number of instances across all variables, tasks and testing sessions whereby the 25-trial mean±1SD was contained within the boundaries established by the regression equations increased as the aggregate scores included more trials. Each equation achieved success in at least 88% of all instances when three trials were included in the sequential mean (95% with five trials). The within-subject variation may offer a means to examine participant-specific changes without having to collect a large number of trials., (Copyright © 2015 Elsevier Ltd. All rights reserved.)