Abstract
Background: Hip muscle weakness is associated with higher peak knee valgus angles (VA) during drop vertical jumps (DVJ) and linked to ACL injury risk. Objective: To determine if isometric strengthening (IST) of the hip extensor, abductor, and external rotator muscle groups would reduce VA exhibited during a DVJ. Methodology: Fourteen female volleyball players (7 training (TG), 7 control (CG), VA≥9˚ during DVJ) participated. Pre- and post-test gluteal, quadriceps and hamstring strength were measured with a digital force gauge. Three-dimensional kinematics were collected during 15 DVJ trials. TG participated in a 6-week IST program that targeted the hip extensor, abductor, and external rotator muscle groups. Two-way mixed ANOVAs compared mean differences of VA and strength. Single-participant analyses examined if athlete-specific adaptations went undetected in the analyses of aggregated data. Results: TG hip extension, abduction, and knee flexion strength increased, respectively, by 20.5%, 27.5% and 23.5% (P<0.05). No group-level changes in VA were detected. Unilateral VA decreased for 5 TG participants, and bilateral VA decreased in 2 TG participants. Conclusions: IST increased isometric hip muscle strength, but its effect on VA is inconclusive based on group-level analyses. Using single-participant designs, future studies should assess IST and/or dynamic resistance/neuromuscular training in a larger sample to determine its effect on ACL injury risk factors.
Highlights
Preventing anterior cruciate ligament (ACL) injuries in female athletes has been heavily researched in recent decades due to high injury rates
At the group-level, there were no significant changes in the mean peak knee valgus angle from pre- to post-test
In the individual-level analyses, five out of seven training group (TG) participants exhibited a significant decrease in peak knee valgus angle on one or both sides from pre- to post-test
Summary
Preventing anterior cruciate ligament (ACL) injuries in female athletes has been heavily researched in recent decades due to high injury rates. There has been an emphasis in the literature placed on sports-related non-contact injuries sustained during landing activities due to the high forces and high risk biomechanical strategies used (Chappell & Limpisvasti, 2008; Ford, Myer, & Hewett, 2003; Hewett et al, 2005; Jacobs, Uhl, Mattacola, Shapiro, & Rayens, 2007; Joseph et al, 2008; Myer, Ford, McLean, & Hewett, 2006). Objective: To determine if isometric strengthening (IST) of the hip extensor, abductor, and external rotator muscle groups would reduce VA exhibited during a DVJ. Conclusions: IST increased isometric hip muscle strength, but its effect on VA is inconclusive based on group-level analyses. Using single-participant designs, future studies should assess IST and/or dynamic resistance/ neuromuscular training in a larger sample to determine its effect on ACL injury risk factors
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