AN INVESTIGATION INTO THE RECOVERY PROCESS OF A MAXIMUM STRETCH-SHORTENING CYCLE FATIGUE PROTOCOL ON DROP AND REBOUND JUMPS THOMAS M. COMYNS, 1,2 ANDREW J. HARRISON, 2 AND LIAM K. HENNESSY 1 1 Strength and Conditioning Department, Irish Rugby Football Union, Dublin, Ireland; 2 Biomechanics Research Unit, Physical Education and Sport Sciences Department, University of Limerick, Limerick, Ireland ABSTRACT Comyns, TM, Harrison, AJ, and Hennessy, LK. An investigation into the recovery process of a maximum stretch-shortening cycle fatigue protocol on drop and rebound jumps. J Strength Cond Res 25(X): 000–000, 2011—The aim of this study was to investigate the recovery process of a maximal stretch-shortening cycle (SSC) fatigue workout on the biomechanical performance of drop jump (DJ) and rebound jump (RBJ) on a force sledge apparatus. Thirteen elite level rugby players performed sledge DJs and RBJs before and 15, 45, 120, and 300 seconds after a maximum SSC fatigue workout. Flight time, ground contact time (CT), peak force, reactive strength index (RSI), and leg-spring stiffness were the dependent variables. The DJ results showed that after 15 seconds recovery, there was a significant reduction in flight time (FT) (p , 0.01), RSI (p , 0.001), peak force (p , 0.01), and leg stiffness (p , 0.001). Similarly, the results for the RBJ indicated that the fatigue workout significantly reduced FT (p , 0.001), peak force (p , 0.01), RSI (p , 0.01), and significantly increased CT (p , 0.05) at the 15-second interval. The results also indicated a potentiation effect at the 300-second interval because of significant increases in RSI, peak force, and leg stiffness (p , 0.05) for the RBJ and significant increases in RSI (p , 0.05), peak force, and leg stiffness (p , 0.01) and a significant decrease in ground CT (p , 0.05) for the DJ. A maximal SSC fatigue workout had both an inhibiting and potentiating effect on DJ and RBJ performance depending on the recovery interval. The efficiency of the SSC function was reduced immediately after the cessation of the fatigue workout. A potentiation effect was evident for both jumps 300 seconds postfatigue. KEY WORDS leg-spring stiffness, plyometric, postactivation potentiation, reactive strength index INTRODUCTION M uscle fatigue is a multifaceted and very complex phenomenon and is believed to involve physiological, biomechanical, and psy- chological components. Fatigue can be defined as any reduction in the force-generating capacity of the total neuromuscular system, regardless of the force required in any given situation (7). Although there may be a causal relationship between muscle fatigue and exercise-related musculoskeletal injuries, there is as yet no definitive research to confirm this or describe the exact way in which fatigue may increase susceptibility to injury. It is generally accepted that muscle fatigue produces discomfort and limits force production (19,20,36), but the effects that fatigue and recovery from fatigue have on other aspects of muscle function are not clear. Complex sports movements are often explosive and powerful in nature and are generally expressed in the form of a stretch-shortening cycle (SSC). The SSC can be defined as an active stretch of a muscle (eccentric contraction), which is immediately followed by a shortening contraction of that same muscle (concentric contraction) thereby causing an enhancement of force development (6). The SSC is crucially important in the performance of many strength, locomotor, and sports activities, and the control of leg-spring and joint stiffness is related to the performance of SSC activities (2,3,22). It has been proposed that the SSC provides a unique and powerful model to study the effects of neuromuscular fatigue on performance (29). Previous research on the effects of fatigue on SSC function has focussed primarily on longer term effects of fatigue and recovery during several days after exhaustive exercise (3–5,33). These and other research studies examining SSC fatigue in long distance running (29), have indicated that longer duration of fatiguing exercise often results in a reversible muscle damage process, which has considerable influence on muscle mechanisms, stretch reflex sensitivity (29), and joint and muscle stiffness (21). Various studies (19,20,25,27,30) induced fatigue by repeated submaximal SSC movements to exhaustion on a sledge and force platform ergometer and found that fatigue caused immediate reductions in SSC performance or longer term losses because of muscle damage. Address correspondence to Dr. Thomas M. Comyns, tomcomyns@ munsterrugby.ie. 0(0)/1–8 Journal of Strength and Conditioning Research Ó 2011 National Strength and Conditioning Association VOLUME 0 | NUMBER 0 | MONTH 2011 | 1 Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.