Time course of changes in jump height was examined to assess whether it was related to changes in the underlying mechanics or muscle activity. In Phase I, 11 novice female students performed 10 maximal jumps for eight consecutive days from two force plates. Jump height, impulse duration (tIMP), and mean vertical ground reaction force (VGRF) were compared using repeated-measures analysis of variance. Jump height was significantly higher (7.7%) on Days 3–8 when compared to Days 1 and 2; tIMP and VGRF were unchanged across days. In a follow-up study (Phase II), 14 novice female students performed 10 maximal jumps for five consecutive days. Electromyographic activity of five leg muscles was recorded to identify the relative onset of each muscle's activity. Using repeated-measures analysis of variance, jump height was significantly higher (4.2%) on Days 2 to 5 compared to Day 1; however, no significant changes were found across Days, for tIMP, VGRF, or the onset of muscle activity. The findings indicate that jump performance can improve rapidly in novice jumpers but the underlying muscle activation remained unchanged.
