The Effect of Plyometric Exercises on Repeated Strength and Power Performance in Elite Karate Athletes

IntroductionCompetitive karate performance is depending on both, technical aspects, and strength and power abilities (Loturco, Artioli, Kobal, Gil, and Franchini, 2014). According to the rules imposed by the World Karate Federation, athlete's main goal is to score by touching the opponent; hence high-intensity actions in punching and kicking techniques are required prior to a response from the opponent (Mori, Ohtani, and Imanaka, 2002). During a typical kumite-karate competition, karate players perform sequential matches interspersed with variable time spaces of inactivity, on a single day (World Karate Federation, 2009). A karate fight is comprised of two 3-min high intensity bouts where repeated unilateral dynamic defensive and offensive kinetic patterns such as frontal, lateral and circular kicks take place. As the attainment of maximum performance is a demand in every competition, muscle power output is of great value for karate athletes aiming to improve the efficacy of specific kinetic patterns demanded for success (Roschel et al., 2009)Post activation potentiation (PAP) has been shown to enhance strength and power production in different activities (Feros, Young, Rice, and Talpey, 2014; Kilduffet al., 2010; Miarka, Del Vechio, and Franchini, 2011; Okuno, Tricoli, Silva, Bertuzzi, Morreira, and Kiss, 2013). PAP constitutes an increase in performance after a high-intensity muscle contraction and has been primarily attributed to increased phosphorylation of the myosin light chains and increased recruitment of motor units (Tillin and Bishop, 2009). However, the conditioning muscle contraction might also induce fatigue and it is the balance between PAP and fatigue that determines the final effect of an explosive activity on performance (Docherty and Hodgson, 2007). The relation between PAP and fatigue is influenced by a combination of factors, such as volume, intensity and type of the conditioning activity (Bogdanis, Tsoukos, Veligekas, Tsolakis, and Terzis, 2014) as well as the recovery period between the conditioning activity and performance (Tillin and Bishop, 2009). The exact protocol of exercise for inducing potentiation is still under investigation. Previous studies have used half squats with varying loads (Gourgoulis, Aggeloussis, Kasimatis, Mavromatis, and Garas, 2003; Mangus et al., 2006), isometric voluntary contractions (French, Kraemer, and Cooke, 2003; Gullich and Schmidtbleicher, 1996; Hamada, Sale, Mac Dougall, and Tarnopolsky, 2003), electrical muscle stimulation (O' Leary, Hope, and Sale, 1997; Trimble, and Harp, 1998) and plyometrics (Masamoto, Larson, Gates, and Faigenbaum, 2003). Plyometric exercises are receiving growing attention as potentiating exercises, probably because of their technical structure similarities with sport-specific skills, and their applicability in real life competition conditions. Interestingly, plyometric exercises have been found to increase performance in kinetic patterns like shot put throwing performance (Terzis, Spengos, Karampatsos, Manta and Georgiadis, 2009; Terzis, Karampatsos, Kyriazis, Kavouras and Georgiadis, 2012) and golf strikes (Read, Miller and Seelig, 2012). Different forms of plyometric contractions, such as drop jumps (Chen, Yu-Han, Hsien-Te, Ching-Fang, and Min- Hsien, 2013; Hilficker, Hubner, Lorenz and Mart, 2007; Saez Saez de Villareal, Gonzalez-Badillo and Izquierdo, 2007), tuck jumps (Donti, Tsolakis, and Bogdanis, 2014; Masamoto et al., 2003; Till and Cooke, 2009; Tsolakis et al., 2011; Turki et al., 2011), vertical hops and bounds (Esformes, Cameron and Bampouras, 2010) at low (Masamoto et al., 2003; Chen et al., 2013; Till and Cooke, 2009) or high-volume or number of repetitions (Chen et al., 2013; Esformes et al., 2010; Saez Saez de Villareal et al., 2007; Tsolakis and Bogdanis, 2012) have been implemented as potentiating exercises but with conflicting results. The discrepancies observed in the aforementioned studies are attributed to differences in potentiating exercises protocols, subsequent activities following PAP, and study population (Chen et al. …