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Female Athletes With Varying Levels of Vertical Stiffness Display Kinematic and Kinetic Differences During Single-Leg Hopping

Justin P. Waxman, Kevin R. Ford, Anh-Dung Nguyen, and Jeffrey B. Taylor

Vertical stiffness may contribute to lower-extremity injury risk; however, it is unknown whether athletes with different stiffness levels display differences in biomechanics. This study compared differences in biomechanics between female athletes (n = 99) with varying stiffness levels during a repetitive, single-leg, vertical hopping task. Vertical stiffness was calculated as the ratio of peak vertical ground-reaction force to maximum center-of-mass displacement. Tertiles were established using stiffness values, and separate 1-way ANOVAs were used to evaluate between-group differences. Stance times decreased, and flight times, ground-reaction force, and stiffness increased, from the low- to high-stiffness group (P < .050). The high-stiffness group displayed: (1) greater lateral trunk flexion (P = .009) and lesser hip adduction (P = .022) at initial ground contact compared to the low- and moderate-stiffness groups, respectively; (2) lesser peak hip adduction compared to the low-stiffness group (P = .040); (3) lesser lateral trunk-flexion (P = .046) and knee-flexion (P = .010) excursion compared to the moderate- and low-stiffness groups, respectively; and (4) greater peak hip-flexion (P = .001), ankle-dorsiflexion (P = .002), and ankle-eversion (P = .038) moments compared to the low-stiffness group. A wide range of variability in stiffness exists within a relatively homogenous population. Athletes with varying stiffness levels display biomechanical differences that may help identify the potential mechanism(s) by which stiffness contributes to injury risk.

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A Comparison of Body Segment Inertial Parameter Estimation Methods and Joint Moment and Power Calculations During a Drop Vertical Jump in Collegiate Female Soccer Players

Sara L. Arena, Kelsey McLaughlin, Anh-Dung Nguyen, James M. Smoliga, and Kevin R. Ford

Athletic individuals may differ in body segment inertial parameter (BSIP) estimates due to differences in body composition, and this may influence calculation of joint kinetics. The purposes of this study were to (1) compare BSIPs predicted by the method introduced by de Leva1 with DXA-derived BSIPs in collegiate female soccer players, and (2) examine the effects of these BSIP estimation methods on joint moment and power calculations during a drop vertical jump (DVJ). Twenty female NCAA Division I soccer players were recruited. BSIPs of the shank and thigh (mass, COM location, and radius of gyration) were determined using de Leva’s method and analysis of whole-body DXA scans. These estimates were used to determine peak knee joint moments and power during the DVJ. Compared with DXA, de Leva’s method located the COM more distally in the shank (P = .008) and more proximally in the thigh (P < .001), and the radius of gyration of the thigh to be further from the thigh COM (P < .001). All knee joint moment and power measures were similar between methods. These findings suggest that BSIP estimation may vary between methods, but the impact on joint moment calculations during a dynamic task is negligible.

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Vertical Jump Biomechanics Altered With Virtual Overhead Goal

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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Standing Pelvic Tilt Is Associated With Dynamic Pelvic Tilt During Running When Measured by 3-Dimensional Motion Capture

Madison S. Mach, Kyle T. Ebersole, Hayley E. Ericksen, Anh-Dung Nguyen, and Jennifer E. Earl-Boehm

Standing pelvic tilt (PT) is related to biomechanics linked with increased risk of injury such as dynamic knee valgus. However, there is limited evidence on how standing PT relates to dynamic PT and whether the palpation meter (PALM), a tool to measure standing PT, is valid against 3-dimensional (3D) motion analysis. The purposes of this study were to (1) determine the criterion validity of the PALM for measuring standing PT and (2) identify the relationship between standing PT and dynamic PT during running. Participants (n = 25; 10 males and 15 females) had their standing PT measured by the PALM and 3D motion analysis. Dynamic PT variables were defined at initial contact and toe off. No relationship between the 2 tools was found. Significant large positive relationships between standing PT and PT at initial contact (r = .751, N = 25, P < .001) and PT at toe off (r = .761, N = 25, P < .001) were found. Since no relationship was found between standing PT measured by the PALM and 3D motion analysis, the PALM is not a valid alternative to 3D motion analysis. Clinicians may be able to measure standing PT and gain valuable information on dynamic PT, allowing clinicians to quickly assess whether further biomechanical testing is needed.