Quadricep and hamstring activation during drop jumps with changes in drop height

Objective: Compare the muscle activation patterns of the quadricep-hamstring during drop jumps with increasing demands of drop heights. Design: Observational. Setting: University biomechanics laboratory. Participants: Fifteen male and eight female college physical education students. Main outcome measures: Electromyographic activity of the rectus femoris (RF) and biceps lemons (BF) during the landing and takeoff phase of drop jumps from 20 to 60-cm heights. The ground contact time, vertical ground reaction force (vGRF), knee flexion angle during ground contact, and jump height after takeoff were also analyzed. Results: The activation of RF was higher in the drop jump from 60-cm than that from 20- and 30-cm (comparing 107.0 +/- 45.9 to 82.3 +/- 30.8 and 88.9 +/- 38.9 %MVIC, P <.05) during the landing phase. Activation of BF remained similar across all drop heights. Drop jump from 60-cm resulted in greater contact time during takeoff phase and peak vGRF, and resulted in greater maximum knee flexion but straighter knee at ground contact than from lower drop heights. Conclusion: At drop height of 60-cm, the altered knee muscular activation and movement patterns may diminish the effectiveness of plyometric training and increase the potential injury risk of knee. (C) 2010 Elsevier Ltd. All rights reserved.