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  • Author: Timothy Jason x
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John J. McMahon, Paul A. Jones, Timothy J. Suchomel, Jason Lake and Paul Comfort

Purpose: The Reactive Strength Index Modified (RSImod) has been recently identified and validated as a method of monitoring countermovement-jump (CMJ) performance. The kinetic and kinematic mechanisms that optimize a higher RSImod score are, however, currently unknown. The purpose of this study, therefore, was to compare entire CMJ force–, power–, velocity–, and displacement–time curves (termed temporal-phase analysis) of athletes who achieve high versus low RSImod scores. Methods: Fifty-three professional male rugby league players performed 3 maximal-effort CMJs on a force platform, and variables of interest were calculated via forward dynamics. The top (high RSImod group) and bottom (low RSImod group) of 20 athletes’ CMJ kinetic- and kinematic-time curves were compared. Results: The high-RSImod group (0.53 ± 0.05 vs 0.36 ± 0.03) jumped higher (37.7 ± 3.9 vs 31.8 ± 3.2 cm) with a shorter time to takeoff (TTT) (0.707 ± 0.043 vs 0.881 ± 0.122 s). This was achieved by a more rapid unweighting phase followed by greater eccentric and concentric force, velocity, and power for large portions (including peak values) of the jump, but a similar countermovement displacement. The attainment of a high RSImod score therefore required a taller, but thinner, active impulse. Conclusions: Athletes who perform the CMJ with a high RSImod, as achieved by high jumps with a short TTT, demonstrate superior force, power, velocity, and impulse during both the eccentric and concentric phases of the jump. Practitioners who include the RSImod calculation in their testing batteries may assume that greater RSImod values are attributed to an increase in these underpinning kinetic and kinematic parameters.

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Jason R. Karp, Jeanne D. Johnston, Sandra Tecklenburg, Timothy D. Mickleborough, Alyce D. Fly and Joel M. Stager

Nine male, endurance-trained cyclists performed an interval workout followed by 4 h of recovery, and a subsequent endurance trial to exhaustion at 70% VO2max, on three separate days. Immediately following the first exercise bout and 2 h of recovery, subjects drank isovolumic amounts of chocolate milk, fluid replacement drink (FR), or carbohydrate replacement drink (CR), in a single-blind, randomized design. Carbohydrate content was equivalent for chocolate milk and CR. Time to exhaustion (TTE), average heart rate (HR), rating of perceived exertion (RPE), and total work (WT) for the endurance exercise were compared between trials. TTE and WT were significantly greater for chocolate milk and FR trials compared to CR trial. The results of this study suggest that chocolate milk is an effective recovery aid between two exhausting exercise bouts.