A comparison between back squat exercise and vertical jump kinematics: implications for determining anterior cruciate ligament injury risk

Brian J Wallace, Thomas W Kernozek, Richard P Mikat, Glenn A Wright, Samuel Z Simons, Kelly L Wallace
Journal of Strength and Conditioning Research 2008, 22 (4): 1249-58
Women are up to eight times more likely than men to suffer an anterior cruciate ligament (ACL) injury, and knee valgus is perhaps the most at-risk motion. Women have been shown to have more knee valgus than men in squatting movements and while landing. The purposes were to investigate whether a relationship exists between lower-extremity frontal plane motions in squatting and landing, whether gender differences exist, and whether squat or hip abduction strength relates to knee valgus while landing. Eleven collegiate Division III soccer players and 11 recreationally trained men were tested for maximal vertical jump height and for squat and hip abduction strength. On the second day of testing, subjects performed light (50% one repetition maximum) and heavy (85%) squat protocols and three landings from their maximal vertical jump height. Pearson's product-moment correlation coefficients and a 2 x 10 factorial analysis of variance with t-test post hoc comparisons (p </= 0.05) were conducted. No strong correlations were shown between any of the squat conditions (eccentric and concentric light, eccentric and concentric heavy) and landing for hip abduction or knee valgus angles. Squat strength did not correlate well with knee valgus angle during landing in men or women. However, hip abduction strength did in women (R = 0.51) but not men (R = 0.10). In hip abduction angle, the eccentric portion of the light squat, eccentric and concentric portions of the heavy squat, and vertical jump landing conditions were different between genders. In knee valgus angle, only the heavy squat conditions were significantly different. Squat strength and observing squat kinematics do not seem to be a method of identifying those at risk while landing; however, hip abduction strength may be in women.

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