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Stefan Sebastian Tomescu, Ryan Bakker, Tyson A.C. Beach and Naveen Chandrashekar

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.

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Harsh H. Buddhadev, Daniel L. Crisafulli, David N. Suprak and Jun G. San Juan

Cycling is commonly prescribed for physical rehabilitation of individuals with knee osteoarthritis (OA). Despite the known therapeutic benefits, no research has examined interlimb symmetry of power output during cycling in these individuals. We investigated the effects of external workload and cadence on interlimb symmetry of crank power output in individuals with knee OA versus healthy controls. A total of 12 older participants with knee OA and 12 healthy sex- and age-matched controls were recruited. Participants performed 2-minute bouts of stationary cycling at 4 workload-cadence conditions (75 W at 60 rpm, 75 W at 90 rpm, 100 W at 60 rpm, and 100 W at 90 rpm). Power output contribution of each limb toward total crank power output was computed over 60 crank cycles from the effective component of pedal force, which was perpendicular to the crank arm. Across the workload-cadence conditions, the knee OA group generated significantly higher power output with the severely affected leg compared with the less affected leg (10% difference; P = .02). Healthy controls did not show interlimb asymmetry in power output (0.1% difference; P > .99). For both groups, interlimb asymmetry was unaffected by external workload and cadence. Our results indicate that individuals with knee OA demonstrate interlimb asymmetry in crank power output during stationary cycling.

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Matt Greig

Kicking is a fundamental skill and a primary noncontact mechanism of injury in soccer, with injury incidence increasing during the latter stages of match-play. Ten male professional soccer players completed a 90-minute treadmill protocol based on the velocity profile of soccer match-play. Preexercise, and at 15-minute intervals, players completed a maximal velocity kick subjected to kinematic analysis at 200 Hz. Preexercise, and at the end of each half, players also completed isokinetic concentric knee extensor repetitions at 180°·s−1, 300°·s−1, and 60°·s−1. Kicking foot speed was maintained at ∼19 m·s−1, with no main effect for exercise duration. In relation to proximal–distal sequencing during the kicking action, there was a significant increase in the duration (but not magnitude) of thigh rotation, with a compensatory decrease in the duration (but not magnitude) of shank rotation during the latter stages of the exercise protocol. In relation to long-axis rotation, pelvic orientation at ball contact was maintained at ∼6°, representing a total pelvic rotation in the order of ∼15° during the kicking action. Peak knee extensor torque at all speeds was also maintained throughout the protocol, such that kinematic modifications are not attributable to a decline in knee extensor strength.

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John R. Harry, Max R. Paquette, Brian K. Schilling, Leland A. Barker, C. Roger James and Janet S. Dufek

This study sought to identify kinetic and electromyographic subphase characteristics distinguishing good from poor jumpers during countermovement vertical jumps (CMVJs), as defined by the reactive strength index (RSI, CMVJ displacement divided by jump time; cutoff = 0.46 m·s−1). A total of 15 men (1.8 [0.6] m, 84.5 [8.5] kg, 24 [2] y) were stratified by RSI into good (n = 6; RSI = 0.57 [0.07] m·s−1) and poor (n = 9; RSI = 0.39 [0.06] m·s−1) performance groups. The following variables were compared between groups using independent t tests (α = .05) and Cohen’s d effect sizes (d ≥ 0.8, large): jump height, propulsive impulse, eccentric rate of force development, and jump time, unloading, eccentric, and concentric subphase times, and average electromyographic amplitudes of 8 lower extremity muscles. Compared with the poor RSI group, the good RSI group exhibited a greater, though not statistically different CMVJ displacement (d = 1.07, P = .06). In addition, the good RSI group exhibited a significantly greater propulsive impulse (P = .04, d = 1.27) and a significantly more rapid unloading subphase (P = .04, d = 1.08). No other significant or noteworthy differences were detected. Enhanced RSI appears related to a quicker unloading phase, allowing a greater portion of the total jumping phase to be utilized generating positive net force. Poor jumpers should aim to use unloading strategies that emphasize quickness to enhance RSI during CMVJ.

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Abigail M. Tyson, Stefan M. Duma and Steven Rowson

Advances in low-cost wearable head impact sensor technology provide potential benefits regarding sports safety for both consumers and researchers. However, previous laboratory evaluations are not directly comparable and do not incorporate test conditions representative of unhelmeted impacts. This study addresses those limitations. The xPatch by X2 Biosystems and the SIM-G by Triax Technologies were placed on a National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform with a Hybrid III neck which underwent impact tests using a pendulum. Impact conditions included helmeted, padded impactor to bare head, and rigid impactor to bare head to represent long- and short-duration impacts seen in helmeted and unhelmeted sports. The wearable sensors were evaluated on their kinematic accuracy by comparing results to reference sensors located at the headform center of gravity. Statistical tests for equivalence were performed on the slope of the linear regression between wearable sensors and reference. The xPatch gave equivalent measurements to the reference in select longer-duration impacts, whereas the SIM-G had large variance leading to no equivalence. For the short-duration impacts, both wearable sensors underpredicted the reference. This error can be improved with increases in sampling rate from 1 to 1.5 kHz. Follow-up evaluations should be performed on the field to identify error in vivo.

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Bradley S. Beardt, Myranda R. McCollum, Taylour J. Hinshaw, Jacob S. Layer, Margaret A. Wilson, Qin Zhu and Boyi Dai

Previous studies utilizing jump-landing biomechanics to predict anterior cruciate ligament injuries have shown inconsistent findings. The purpose of this study was to quantify the differences and correlations in jump-landing kinematics between a drop-jump, a controlled volleyball-takeoff, and a simulated-game volleyball-takeoff. Seventeen female volleyball players performed these 3 tasks on a volleyball court, while 3-dimensional kinematic data were collected by 3 calibrated camcorders. Participants demonstrated significantly increased jump height, shorter stance time, increased time differences in initial contact between 2 feet, increased knee and hip flexion at initial contact and decreased peak knee and hip flexion for both left and right legs, and decreased knee–ankle distance ratio at the lowest height of midhip for the 2 volleyball-takeoffs compared with the drop-jump (P < .05, Cohen’s d z ≥ 0.8). Significant correlations were observed for all variables between the 2 volleyball-takeoffs (P < .05, ρ ≥ .6) but were not observed for most variables between the drop-jump and 2 volleyball-takeoffs. Controlled drop-jump kinematics may not represent jump-landing kinematics exhibited during volleyball competition. Jump-landing mechanics during sports-specific tasks may better represent those exhibited during sports competition and their associated risk of anterior cruciate ligament injury compared with the drop-jump.

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Yuji Matsuda, Yoshihisa Sakurai, Keita Akashi and Yasuyuki Kubo

Center of mass (CoM) velocity variation in swimming direction is related to swimming performance and efficiency. However, it is difficult to calculate the CoM velocity during swimming. Therefore, we aimed to establish a practical estimation method for the CoM velocity in swimming direction during front crawl swimming with underwater cameras. Ten swimmers were recorded during front crawl swimming (25 m, maximal effort) using a motion capture system with 18 underwater and 9 land cameras. Three CoM velocity estimation methods were constructed (single-hip velocity, both-hips velocity, and both-hips velocity with simulated arm velocity correction). Each model was validated against the actual CoM velocity. The difference between the single-hip velocity and the actual CoM velocity in swimming direction was significantly larger compared with that of the other 2 models. Furthermore, the accuracy of CoM velocity estimation was increased when both-hips velocity was corrected using the simulated arm velocity. The method allowed estimation of the CoM velocity with only 2 underwater cameras with a maximal difference of 0.06 m·s−1. This study established a novel and practical method for the estimation of the CoM velocity in swimming direction during front crawl swimming.

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Tzu-Chieh Liao, Joyce H. Keyak and Christopher M. Powers

The primary purpose of this study is to determine whether recreational runners with patellofemoral pain (PFP) exhibit greater peak patella cartilage stress compared with pain-free runners. A secondary purpose was to determine the kinematic and/or kinetic predictors of peak patella cartilage stress during running. A total of 22 female recreational runners (12 with PFP and 10 pain-free controls) participated in this study. Patella cartilage stress profiles were quantified using subject-specific finite element models simulating the maximum knee flexion angle during the stance phase of running. Input parameters to the finite element model included subject-specific patellofemoral joint geometry, quadriceps muscle forces, and lower-extremity kinematics in the frontal and transverse planes. Tibiofemoral joint kinematics and kinetics were quantified to determine the best predictor of stress using stepwise regression analysis. Compared with the pain-free runners, those with PFP exhibited greater peak hydrostatic pressure (PFP vs control: 21.2 [5.6] MPa vs 16.5 [4.6] MPa) and maximum shear stress (PFP vs control: 11.3 [4.6] MPa vs 8.7 [2.3] MPa). Knee external rotation was the best predictor of peak hydrostatic pressure and peak maximum shear stress (38% and 25% of variances, respectively), followed by the knee extensor moment (21% and 25% of variances, respectively). Runners with PFP exhibit greater peak patella cartilage stress during running compared with pain-free individuals. The combination of knee external rotation and a high knee extensor moment best predicted the elevated peak stress during running.

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Yumeng Li, Rumit S. Kakar, Marika A. Walker, Li Guan and Kathy J. Simpson

The upper trunk–pelvic coordination patterns used in running are not well understood. The purposes of this study are to (1) test the running speed effect on the upper trunk–pelvis axial rotation coordination and (2) present a step-by-step guide of the relative Fourier phase algorithm, as well as some further issues to consider. A total of 20 healthy young adults were tested under 3 treadmill running speeds using a 3-dimensional motion capture system. The upper trunk and pelvic segmental angles in axial rotation were calculated, and the coordination was quantified using the relative Fourier phase method. Results of multilevel modeling indicated that running speed did not significantly contribute to the changes in coordination in a linear pattern. A qualitative template analysis suggested that participants displayed different change patterns of coordination as running speed increased. Participants did not significantly change the upper trunk and pelvis coordination mode in a linear pattern at higher running speeds, possibly because they employed different motion strategies to achieve higher running speeds and thus displayed large interparticipant variations. For most of our runners, running at a speed deviated from the preferred speed could alter the upper trunk–pelvis coordination. Future studies are still needed to better understand the influence of altered coordination on running performance and injuries.

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ZáNean McClain and E. Andrew Pitchford