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Kristof Kipp, Michael T. Kiely, Matthew D. Giordanelli, Philip J. Malloy and Christopher F. Geiser

-sectional differences and monitoring longitudinal changes in maximal dynamic lower-extremity performance. Although the RSI provides simple insight into dynamic lower-extremity performance during a DJ, not much is known about its biomechanical determinants. Beyond the variables of jump height and ground-contact time

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Daniel M. Grindle, Lauren Baker, Mike Furr, Tim Puterio, Brian Knarr and Jill Higginson

while they work. Currently, there is a lack of research on the gait biomechanics of walking workstation users. Working while walking may alter movement patterns, as previous studies have demonstrated that the performance of a secondary task during walking alters gait 12 – 14 especially in older

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Kimmery Migel and Erik Wikstrom

to contribute to aberrant gait biomechanics observed in those with CAI. More specifically, those with CAI demonstrate excessive inversion at heel strike and throughout stance as well as excessive inversion and plantar flexion in the swing phase of gait. 2 These impairments increase the risk of

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Kevin R. Ford, Anh-Dung Nguyen, Eric J. Hegedus and Jeffrey B. Taylor

Virtual environments with real-time feedback can simulate extrinsic goals that mimic real life conditions. The purpose was to compare jump performance and biomechanics with a physical overhead goal (POG) and with a virtual overhead goal (VOG). Fourteen female subjects participated (age: 18.8 ± 1.1 years, height: 163.2 ± 8.1 cm, weight 63.0 ± 7.9 kg). Sagittal plane trunk, hip, and knee biomechanics were calculated during the landing and take-off phases of drop vertical jump with different goal conditions. Repeated-measures ANOVAs determined differences between goal conditions. Vertical jump height displacement was not different during VOG compared with POG. Greater hip extensor moment (P < .001*) and hip angular impulse (P < .004*) were found during VOG compared with POG. Subjects landed more erect with less magnitude of trunk flexion (P = .002*) during POG compared with VOG. A virtual target can optimize jump height and promote increased hip moments and trunk flexion. This may be a useful alternative to physical targets to improve performance during certain biomechanical testing, screening, and training conditions.

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Jay L. Alberts and Susan M. Linder

The acute and long-term effects of concussive and subconcussive head impacts on brain health have gained tremendous attention over the past five years. The treatment and management of concussion involves multiple providers from multiple disciplines and backgrounds. Varied backgrounds and approaches to assessing cognitive and motor function before and post-concussion are limiting factors in the efficient and effective management of concussion as discipline-specific rating scales and assessments serve as a barrier to effective patient hand-offs between providers. Combining principles of motor behavior with biomechanical approaches to data analysis has the potential to improve the continuity of care across the multiple providers managing athletes with concussion. Biomechanical measures have been developed and validated using mobile devices to provide objective and quantitative assessments of information processing, working memory, set switching, and postural stability. These biomechanical outcomes are integral to a clinical management algorithm, the Concussion Care Path, currently used across the Cleveland Clinic Health System. The objective outcomes provide a common data set that all providers in the spectrum of care can access which facilitates communication and the practice of medicine and in understanding the acute and long-term effects of concussion and subconcussive exposure on neurological function.

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Giancarlo Condello, Thomas W. Kernozek, Antonio Tessitore and Carl Foster

This study aimed to investigate biomechanical parameters during a change-of-direction task in college soccer players. Fourteen male and 12 female players performed a 10-m sprint with a 60° change of direction at 5 m. Vertical and mediolateral groundreaction force (GRF) and contact time were measured by having the subjects run in both directions while contacting a force plate with either their preferred (kicking) or nonpreferred leg. Using the midpoint between 2 pelvic markers, further parameters were evaluated: performance cutting angle and horizontal distance. Relationships between parameters, sex, and leg preference were analyzed. Significant correlations emerged between vertical and mediolateral GRF (r = .660–.909) and between contact time and performance cutting angle (r = –.598 to –.793). Sex differences were found for mediolateral GRF (P = .005), performance cutting angle (P = .043), and horizontal distance (P = .020). Leg differences were observed for vertical GRF (P = .029), performance cutting angle (P = .011), and horizontal distance (P = .012). This study showed that a sharper change of direction corresponded to a longer contact time, while no relationships were found with GRF. Moreover, measuring the angle revealed that the real path traveled was different from the theoretical one, highlighting the performance of sharper or more rounded execution. In conclusion, this study showed that specific biomechanical measurements can provide details about the execution of a change of direction, highlighting the ability of the nonpreferred leg to perform better directional changes.

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Bernard Liew, Susan Morris and Kevin Netto

The aim of this systematic review was to evaluate the impact of bilaterally symmetrical backpack systems borne on the posterior trunk on walking biomechanics, as backpacks represent the most prevalent method of load carriage in the military and civilian population. A search of electronic databases was performed for studies that only investigated posteriorly-borne backpack carriage during level-grade walking (treadmill and over ground). Methodology of studies was assessed, and both meta-analysis and qualitative synthesis were completed. Fifty-four studies were included in this review. In summary, the available literature showed that backpack carriage in walking was associated with an increased trunk flexion angle, increased hip and ankle range of motion, increased vertical and horizontal ground reaction force, increased cadence, and reduced stride length. Several variations in backpack carriage protocols could explain between-study variations in results, including: walking speed, backpack carriage skill level, the use of a hip belt, and posterior displacement of the load away from the trunk. The findings of this systematic review will inform backpack carriage practices in the area of injury risk assessment and physical performance enhancement.

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Declan A. Patton, Andrew S. McIntosh and Svein Kleiven

Biomechanical studies of concussions have progressed from qualitative observations of head impacts to physical and numerical reconstructions, direct impact measurements, and finite element analyses. Supplementary to a previous study, which investigated maximum principal strain, the current study used a detailed finite element head model to simulate unhelmeted concussion and no-injury head impacts and evaluate the effectiveness of various tissue-level brain injury predictors: strain rate, product of strain and strain rate, cumulative strain damage measure, von Mises stress, and intracranial pressure. Von Mises stress was found to be the most effective predictor of concussion. It was also found that the thalamus and corpus callosum were brain regions with strong associations with concussion. Tentative tolerance limits for tissue-level predictors were proposed in an attempt to broaden the understanding of unhelmeted concussions. For the thalamus, tolerance limits were proposed for a 50% likelihood of concussion: 2.24 kPa, 24.0 s−1, and 2.49 s−1 for von Mises stress, strain rate, and the product of strain and strain rate, respectively. For the corpus callosum, tolerance limits were proposed for a 50% likelihood of concussion: 3.51 kPa, 25.1 s−1, and 2.76 s−1 for von Mises stress, strain rate, and the product of strain and strain rate, respectively.

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Saira Chaudhry, Dylan Morrissey, Roger C. Woledge, Dan L. Bader and Hazel R.C. Screen

Triceps surae eccentric exercise is more effective than concentric exercise for treating Achilles tendinopathy, however the mechanisms underpinning these effects are unclear. This study compared the biomechanical characteristics of eccentric and concentric exercises to identify differences in the tendon load response. Eleven healthy volunteers performed eccentric and concentric exercises on a force plate, with ultrasonography, motion tracking, and EMG applied to measure Achilles tendon force, lower limb movement, and leg muscle activation. Tendon length was ultrasonographically tracked and quantified using a novel algorithm. The Fourier transform of the ground reaction force was also calculated to investigate for tremor, or perturbations. Tendon stiffness and extension did not vary between exercise types (P = .43). However, tendon perturbations were significantly higher during eccentric than concentric exercises (25%–40% higher, P = .02). Furthermore, perturbations during eccentric exercises were found to be negatively correlated with the tendon stiffness (R 2 = .59). The particular efficacy of eccentric exercise does not appear to result from variation in tendon stiffness or extension within a given session. However, varied perturbation magnitude may have a role in mediating the observed clinical effects. This property is subject-specific, with the source and clinical timecourse of such perturbations requiring further research.

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Brian A. Blanksby, Jennifer R. Simpson, Bruce C. Elliott and Keith McElroy

Because turning can account for one-third of breaststroke race time in 25 m pools, it is possible that enhancing turning techniques can improve performance significantly. Underwater video cameras and a force platform were used to analyze turning techniques of 23 age-group breaststrokers during three 50 m push-start, maximum-effort swims. The criterion measure was the time elapsed between passing the 5 m mark on the approach and departure from the wall (5 m round-trip time [RTT]). Correlations revealed significant commonality of variance (p < .01) between the 5 m RTT and the 2.5 m RTT, 50 m time, average single-stroke velocity, peak reaction force, pivot time, impulse, peak horizontal velocity off the wall, arm and leg split-stroke resumption distances, surfacing distance, surfacing time, and horizontal velocity, height, and mass of the subjects. All swimmers achieved a net gain at the turn in that the mean 5 m RTT (20% of the distance) represented 18.26% of the total swimming time. Following stepwise regression, a successful turn was predicted by the equation 17.113 - 0.322 surfacing distance - 0.036 height - 0.723 surfacing horizontal velocity + 0.723 pivot time - 0.65 peak horizontal velocity.