The Acute Effect of the Type and Intensity of Dynamic Contraction on Performance Indicators and Some Electromyographic Variables of Vertical Jump in Track and Field Athletes

The aim of this study was to examine the temporary effect of type and intensity of dynamic contractions on some electromyography and performance variables in professional track and field athletes. 9 subjects randomly performed one of the four protocols in 4 different days: usual warm-up (control group), warm-up and a set of four repetitions of negative half squatting (120% of 1RM), warm-up and a set of six repetitions of power-strength half squatting (80% of 1RM) and warm-up and a set of twelve repetitions of power-velocity half squatting (40% of 1RM). 7 minutes after each protocol, the subjects performed the maximum voluntary isometric contraction (MVIC) and vertical jump test. Simultaneously, EMG activity of the rectus femoris, vastus lateralis and biceps femoris muscles was registered in MVIC test and concentric phase of vertical jump. Then, maximum muscle activity and RMS/MVC ratio index was derived from EMG data. The results showed that vertical jump, the maximum muscle activity and RMS/MVC ratio significantly increased after negative and power-strength half squatting protocols compared with the control group (P≤0.05). Furthermore, negative half squatting protocol had more increase than power-strength half squatting (P≤0.05). So the special warm-up including half squatting with supra-maximal and close to the maximum intensities can improve vertical jump performance compared with the usual warm-up.