Search Results

The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. Sixteen female high school volleyball players performed the drop vertical jump from three different drop heights. Surface electromyography of the quadriceps and hamstrings were collected during the movement trials. As the drop height increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05). However, the hamstrings activation showed no similar increases relative to drop height. Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio of the hamstrings relative to quadriceps before landing may represent altered dynamic knee stability and may contribute to the increased risk of ACL injury in female athletes.

Context: Women’s volleyball requires frequent and repetitive jumping that when performed with altered biomechanics, including kinematic or kinetic asymmetry, may place the athlete at high risk for injury. This study identified and analyzed lower-extremity biomechanical asymmetries in college women’s volleyball players during standard and sport-specific double-leg landing tasks. Design: Cross-sectional laboratory study. Methods: Eighteen female college volleyball players were analyzed using standard 3D motion capture techniques during a drop vertical jump and an unanticipated lateral reactive jump task. Repeated-measures multivariate analysis of variance identified asymmetries in kinematic and kinetic variables of each task. Results: Average symmetry indices ranged from 9.3% to 31.3% during the drop vertical jump and 11.9% to 25.6% during the reactive jump task. During the drop vertical jump, the dominant limb exhibited lower knee abduction moments (P = .03), ankle dorsiflexion moments (P = .02), ankle eversion moments (P = .003) and vertical ground reaction forces (P = .03), and greater ankle inversion moments (P = .001). Both kinematic (λ = 0.27, P = .03) and kinetic (λ = 0.12, P = .008) asymmetries were identified during the reactive jump task. The dominant limb exhibited greater peak knee flexion (P = .003) and ankle dorsiflexion (P = .02) angles, and greater ankle dorsiflexion (P = .005) and inversion (P = .03) moments than the nondominant limb. Conclusions: These asymmetries observed during double-leg landing tasks may predispose volleyball athletes to unilaterally higher ground reaction or muscle forces and ultimately a greater risk of injury during landing.

Context: Biofeedback training enables an athlete to alter biomechanical and physiological function by receiving biomechanical and physiological data concurrent with or immediately after a task. Objective: To compare the effects of 2 different modes of real-time biofeedback focused on reducing risk factors related to anterior cruciate ligament injury. Design: Randomized crossover study design. Setting: Biomechanics laboratory and sports medicine center. Participants: Female high school soccer players (age 14.8 ± 1.0 y, height 162.6 ± 6.8 cm, mass 55.9 ± 7.0 kg; n = 4). Intervention: A battery of kinetic- or kinematic-based real-time biofeedback during repetitive double-leg squats. Main Outcome Measures: Baseline and posttraining drop vertical jumps were collected to determine if either feedback method improved high injury risk landing mechanics. Results: Maximum knee abduction moment and angle during the landing was significantly decreased after kinetic-focused biofeedback (P = .04). The reduced knee abduction moment during the drop vertical jumps after kinematic-focused biofeedback was not different (P = .2). Maximum knee abduction angle was significantly decreased after kinetic biofeedback (P < .01) but only showed a trend toward reduction after kinematic biofeedback (P = .08). Conclusions: The innovative biofeedback employed in the current study reduced knee abduction load and posture from baseline to posttraining during a drop vertical jump.

Context: Hip-focused interventions are aimed to decrease frontal plane knee loading related to anterior cruciate ligament injuries. Whether a preferred hip landing strategy decreases frontal plane knee loading is unknown. Objective: To determine if a preferred hip landing strategy during a drop vertical jump (DVJ) is utilized during a single-leg landing (SLL) task and whether differences in frontal plane knee loading are consistent between a DVJ and an SLL task. Design: Descriptive laboratory study. Setting: Research laboratory. Participants: Twenty-three collegiate, female soccer players. Main Outcome Measures: Participants were dichotomized into a hip (HIP; n = 9) or knee/ankle (KA; n = 14) strategy group based on the percentage distribution of each lower extremity joint relative to the summated moment (% distribution) during the DVJ. Separate 1-way analysis of variances examined the differences in joint-specific % distribution and external knee abduction moment between the HIP and KA groups. Results: The HIP group had significantly greater % distribution of hip moment and less % distribution of knee moment compared with the KA group during the DVJ and SLL. External knee abduction moment was also significantly less in the HIP group compared with the KA group during the DVJ. Conclusions: Female soccer athletes who land with a preferred hip strategy during a DVJ also land with a preferred hip strategy during an SLL. The preferred hip strategy also resulted in less external knee abduction moments during the DVJ. Clinical Relevance: Targeting the neuromuscular control of the hip extensor may be useful in reducing risk of noncontact anterior cruciate ligament injuries.

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.

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.

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.

Context: Physical changes following activity are well documented, but there is limited information about self-reported outcomes around competitive matches. High training volumes and poor recovery could predispose athletes to overuse injury. The purpose of this study was to identify the changes in daily athlete health measures before, during, and after the day of each match in high- and low-volume groups. Design: Prospective cohort. Methods: Fifty-five soccer athletes (age: 19.8 [1.2] y, 26 males, 29 females) provided daily measures of readiness, physical fatigue, mental stress, sleep quality, and soreness intensity match days, days 1 (D01) and 2 (D02) following matches, and standard practice days. Participants were grouped into high volume and low volume, based off the minutes played during the season. Results: Soreness increased, readiness decreased, and fatigue increased on D01 compared with match days (P < .008) in the high-volume group. Between groups, the high-volume group demonstrated higher soreness on D01 and D02, lower readiness on D01 and D02, and lower fatigue on D01, compared with the low-volume group (P < .008). Conclusions: Soccer athletes demonstrate significant changes in self-reported athlete health variables around competitive matches. These changes are similar to physical outcomes, potentially indicating that the athlete health variables may be used to track athlete recovery from competition, potentially limiting the impact of overuse injuries.