The Effect of Type and Intensity of Voluntary Contractions on some of Vertical Jump's Electrophysiological Variables in Track and Field Athletes

The purpose of this study was to determine the effect of type and intensity of voluntary contractions on some of vertical jump's electrophysiological variables. The subjects were 12 trained track and field athletes. The subjects performed one set of dynamic or isometric half-squat using maximal (MD= Maximal Dynamic half-squat, MI= Maximal Isometric half-squat for 7 seconds), submaximal (SD= Submaximal Dynamic half-squat, SI= Submaximal Isometric half-squat for 4 seconds), and a control (C) warm up condition on randomized separating conditions over the course of different 5 days. After a 5 minutes post-protocols, the subjects completed a vertical jump test (VJ). The electromyographic (EMG) activity of quadriceps (Qc) and hamstring (H) were recorded during the concentric phase of the jumps. A one way ANOVA with repeated measures on the one factor was used to analyze the data. The results of this study indicated that the vertical jump height had improved significantly (p ≤ 0.05) after MD (10.58%), SD (10.53%), and SI (7.79%) protocols compared to C. No significant differences were found among the repeated measures in Qc and H activity (p > 0.05). It is concluded that the use of a specific warmup that includes half-squats, performed with submaximal to maximal intensity, improves VJ performance that seems to be more related to the intramuscular changes.