Effect of Drop Height on Lower Extremity Biomechanical Measures in Female Athletes

Abstract

PURPOSE: The drop vertical jump (DVJ) is an exercise in which a drop landing is followed by a maximal height vertical jump, inducing a stretch-shortening sequence in lower extremity extensor muscles. The performance of DVJ at different heights has been examined in male, but not female, athletes. The purpose of this study was to identify alterations in landing and takeoff phase joint moments and muscle activation patterns across different drop heights. The primary hypothesis was that knee extensor moment and quadriceps muscle activation would increase with increased drop heights in female athletes. METHODS: 16 female, high school volleyball players volunteered to participate in the study. Maximum effort DVJ were performed from three heights (15cm, 30cm and 45cm), in random order. Three trials were collected from each height. Surface electromyography (EMG) was recorded from the semitendinosus, biceps femoris, vastus medialis, vastus lateralis and rectus femoris muscles. A 10 camera motion analysis system and two force plates were used to calculate joint moments during the DVJ. Normalized EMG (% maximum voluntary contraction) and lower extremity extensor moments were averaged over the landing and takeoff phases. A repeated measures ANOVA was used to analyze effect of drop height on measured variables (p<0.05). RESULTS: During the landing phase, ankle, knee and hip extensor moments increased as drop height increased (p<0.05). Quadriceps muscle activation (p<0.05) increased but hamstrings activation did not. No changes in jump height, joint moments or EMG were observed during takeoff. CONCLUSIONS: The observed increases in joint moments and quadriceps muscle activation were likely related to the greater demand on the lower extremity to decelerate the body center of mass when landing from greater height. During the takeoff, however, no biomechanical changes were observed. The absence of increased hamstrings muscle activation and overall low amplitude during the landing phase is of interest, and should be examined further, especially in relation to the tendency of female athletes to preferentially activate the quadriceps relative to the hamstrings.