Assessing Plyometric Ability during Vertical Jumps Performed by Adults and Adolescents.

Brandon Snyder,Shawn Munford,Chris Connaboy,Shala Davis,Hugh Lamont,Gavin Moir

doi:10.3390/sports6040132

Abstract

The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players (age: 16.5 ± 0.7 years) performed a CMJ and a DJ from a height of 0.40 m. Jump height (JH), contact time, normalized work (WNORM), and power output (PONORM) during the absorption and propulsion phases were calculated from force platforms and 3-D motion analysis data. Plyometric ability was assessed using the modified reactive strength index (RSIMOD during CMJ) and the reactive strength index (RSI during DJ) as well as three indices using propulsion time, propulsion work (PWI), and propulsion power. Adults jumped significantly higher than adolescents (mean difference [MD]: 0.05 m) while JH (MD: 0.05 m) and ground contact time (MD: 0.29 s) decreased significantly from CMJ to DJ. WNORM (MD: 4.2 J/kg) and PONORM (MD: 24.2 W/kg) during the absorption phase of CMJ were significantly less than these variables during the propulsion phases of the jumps. The reactive strength index variants increased significantly from the CMJ to DJ (MD: 0.23) while all other plyometric indices decreased significantly. Neither RSIMOD nor RSI contributed significantly to the prediction of JH during CMJ and DJ, respectively, while PWI was able to explain ≥68% of the variance in JH. Variants of the reactive strength index do not reflect the changes in mechanical variables during the ground contact phase of CMJ and DJ and may not provide an accurate assessment of plyometric ability during different vertical jumps.

Highlights

Plyometric training has been shown to be an effective means of improving measures of athletic ability including vertical jump, sprint running, and change of direction tasks [1,2]
It was found that ground contact times decreased significantly from the countermovement jumps (CMJ) to the drop jumps (DJ) task in both age groups as a result of significant reductions in the duration of both the absorption and propulsion phases
Other researchers have noted that the technique used during a DJ task can affect jump height with the execution of a DJ with very brief ground contact times not necessarily resulting in greater jump heights [23,34]

Summary

Introduction

Plyometric training has been shown to be an effective means of improving measures of athletic ability including vertical jump, sprint running, and change of direction tasks [1,2]. Plyometric exercise such as countermovement jumps (CMJ) and drop jumps (DJ) incorporate the stretch-shortening cycle (SSC) whereby the musculotendinous units are initially lengthened prior to shortening up to takeoff [3]. Plyometric ability, defined as the ability to utilize the SSC during movement tasks, has been shown to be a trainable characteristic with improvements realized following a period of resistance training [8,9].

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Conclusion