Purpose: The aim of this study was to determine the acute effects of unilateral and bilateral squats performing (postactivation potentiation) on vertical jump performance and EMG
activity of the selected muscles in athlete men during a vertical jumping.
Material and Methods: The subjects were 20 trained athlete men (10 volleyball players, 10 basketball players) with the characteristics of age: 20/94± 2/56 years, weight: 74/64± 6/72 kg, height: 180± 6/55 cm) that voluntary participate in this study. the subjects performed each of the three protocols: 1. Common warm up (the running on the treadmill with the speed of 9 km/h in 5 minutes and stretch movements on 3 minutes), 2. warm up and 1 set with two repetitions of dynamic bilateral half-squat with 90% 1RM, 3. warm up and 1 set with two repetitions of dynamic unilateral half-squat with 90% 1RM in three different
days and randomized condition. in 5 minutes of recovery from each protocol, subjects were examined with the vertical jump test, and EMG activity of quadriceps and hamstring muscles were recorded in concentric phases of the jumping and during maximum voluntary contraction (MVC). the RMS/MVC index was derived from muscle's EMG signals. One-way ANOVA with repeated measures was used to data analysis.
Results: The vertical jumping height have significantly improved after the second and third protocols (post-activation potentiation) compared to common traditional warm up (P= 0/043, 0/018 respectively), but no significant differences was found among the quadriceps and hamstring muscles electrical activity in three different conditions (P≥0/05).
Conclusion: The specific warm up method via using unilateral or bilateral half-squat probably can improve the athlete's subsequent vertical jumping performance. these changes are related to intramuscular variations.