The effect of loading on the enhancement of counter movement jumps (CMJ) over three consecutive trials
Date
2003
Authors
Robbins, Daniel William
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Abstract
The purpose of this study was to investigate the acute effects on six dependent variables of neuromuscular activation through maximal voluntary isometric contractions (MVIC) performed in the squat position. The MVIC's were performed at a knee joint angle of 100 degrees and held for 7 seconds. The six dependent variables were vertical jump height (VJH), peak force (PF), rate to peak force (RPF), peak power (PP), peak acceleration (PA) and peak velocity (PV). Furthermore, correlations were performed between relative and absolute strength and the six performance measurements. Sixteen trained males (age: X = 23.06, SD= 2.70; weight: X = 84 kg, SD= 7.86) experienced with back squats participated in the study. Each subject took part in one familiarization session and two testing protocols. The familiarization session was designed to determine if learning effects were present with respect to the six performance measurements and the MVIC. Both testing protocols consisted of 4 sets of 5 countermovement jumps ( CMJ) performed with 8-min intervals. The single difference between the two protocols was the execution of a 7-s MVIC performed 4 minutes prior to the execution of CMJ in protocol 1. A repeated-measures MANOVA was performed. Application of the Bonferroni procedure indicated that no significant differences occurred between protocol 1 and 2, nor did significance occur linearly across the four sets of CMJ. Only one significant correlation between relative strength and performance enhancement or absolute strength and performance enhancement was found. A significant correlation existed between absolute strength (MVIC) and PA using mean values (p< 0.01 ). No significant correlations were found with respect to absolute strength and maximal values nor were any significant correlations found with respect to relative strength and either mean or maximal post MVIC values.