Affiliation:
1. 1Texas Tech University
2. 2The University of Memphis
3. 3University of Nevada
4. 4Texas Tech University Health Sciences Center
Abstract
This study sought to identify kinetic and electromyographic subphase characteristics distinguishing good from poor jumpers during countermovement vertical jumps (CMVJs), as defined by the reactive strength index (RSI, CMVJ displacement divided by jump time; cutoff = 0.46 m·s−1). A total of 15 men (1.8 [0.6] m, 84.5 [8.5] kg, 24 [2] y) were stratified by RSI into good (n = 6; RSI = 0.57 [0.07] m·s−1) and poor (n = 9; RSI = 0.39 [0.06] m·s−1) performance groups. The following variables were compared between groups using independentttests (α = .05) and Cohen’sdeffect sizes (d ≥ 0.8, large): jump height, propulsive impulse, eccentric rate of force development, and jump time, unloading, eccentric, and concentric subphase times, and average electromyographic amplitudes of 8 lower extremity muscles. Compared with the poor RSI group, the good RSI group exhibited a greater, though not statistically different CMVJ displacement (d = 1.07,P = .06). In addition, the good RSI group exhibited a significantly greater propulsive impulse (P = .04,d = 1.27) and a significantly more rapid unloading subphase (P = .04,d = 1.08). No other significant or noteworthy differences were detected. Enhanced RSI appears related to a quicker unloading phase, allowing a greater portion of the total jumping phase to be utilized generating positive net force. Poor jumpers should aim to use unloading strategies that emphasize quickness to enhance RSI during CMVJ.
Subject
Rehabilitation,Orthopedics and Sports Medicine,Biophysics
Cited by
27 articles.
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