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Team sports frequently necessitate intermittent brief, high intensity bouts of activity, separated by extended phases of rest or low intensity exercise (Spencer et al., 2004; Bishop and Edge, 2006). Time motion analysis of rugby union has shown that although high intensity activity only accounts for 12-13% of game time for the forwards and 4.5% of game time for the backs (Deutsch et al., 2007), sprint exertions have been thought to contribute to the most decisive phases of play in intermittent-sprint sports (Reilly et al., 2000; Oliver et al., 2007). Additionally, law variations have purported to amplify the excitement of rugby union by keeping the ball in play for longer periods of time (International Rugby Board). As a result, performance analysis studies of rugby union have witnessed increased periods of high-intensity activity, combined with decreased periods of recovery in recent times (Duthie et al. 2006; Deutsch et al. 2007). Consequently, a desirable fitness component for team-sport athletes is the capacity to execute maximal sprints with a short recovery period for a prolonged period of time (Bishop et al., 2001; Bishop and Edge, 2006; Oliver et al., 2007); this has been termed repeated-sprint ability (RSA) (Dawson et al. 1993). Despite this understanding of RSA and its contribution to overall team-sport performance, the physiological qualities that contribute to RSA have yet to be adequately elucidated.
Muscular leg strength is a physiological ability thought to facilitate repeated-sprint ability (Alexander, 1989; Dowson, 1998). However, the majority of studies have merely examined the relationship between muscular leg strength and a single-sprint, rather than repeated-sprint ability (Thorland et al., 1987; Alexander, 1989; Dowson et al., 1998; Baker and Nance, 1999; Cronin and Hansen, 2005). Of the few studies that have compared repeated sprint ability with leg strength (Newman et al., 2004; Kin-Isler, 2008), isokinetic strength measures have been employed, which poorly reflect the movement patterns experienced in rugby union (Duthie et al., 2006). Therefore, one area of study for the current investigation is the relationship between muscular leg strength and brief repeated-sprint ability, using a multi-joint strength measure.
Furthermore, literature has acknowledged that the length of recovery between sprints can significantly augment metabolic fatigue (Gaitanos et al., 1993; Bishop and Edge., 2006; Oliver et al., 2007), and thus, the relationship between leg strength and RSA. Although studies on RSA have been inclined to implement brief recovery periods (<30 s) in their protocols (Dawson et al., 1991; Newman et al., 2004; Edge et al., 2006; McGawley and Bishop, 2006; Spencer et al., 2008), a study by Bishop and Edge (2006) recently highlighted that many of the recovery patterns experienced during team sports are prolonged in nature (>60s), suggesting that longer periods of recovery could better reflect a longer period of a team-sport match. To the author's knowledge, no study has investigated the correlation between muscular leg strength and prolonged repeated sprint ability.
When examining specific populations i.e. rugby players, it is vital to ensure validity and specificity when designing repeated-sprint protocols. This includes recovery mode, of which active recovery appears the most valid when assessing team sport athletes (Spencer et al., 2004 Jougla et al., 2009). Second, the length of each sprint must be considered, although the majority of authors have implemented 6 second sprints (Gaitanos et al., 1993; Dawson et al., 1997; Edge et al., 2005; Bishop et al., 2005), shorter distances appear to more accurately reflect the sprint distances executed in team sports (Spencer et al., 2004; Duthie et al., 2006 and Deutsch et al., 2007). With regards to the amount of sprints performed, 5-10 sprints appear to most accurately represent a brief intense period of play (Spencer et al., 2004), and have most commonly been used within the literature (Gaitanos et al., 1993; Dawson et al., 1997; Bishop and Spencer., 2004; Edge et al., 2005; Bishop et al., 2004; Spencer et al., 2006; Oliver et al., 2007; Spencer et al., 2008). A final point to consider is the mode of exercise performed, of which RSA studies have been inclined to use cycle ergometry (Gaitanos et al., 1993; Dawson et al., 1997; Bishop and Spencer, 2004; Edge et al., 2005; Bishop et al., 2004), which for most sports, provides an inaccurate means of testing athletes that primarily execute over-ground sprints in their respective sports (Fitzimmons et al., 1993; Bishop et al., 2001; Oliver et al., 2007)
Recently, explosive power has been considered a possible predictor of repeated-sprint performance (Dowson et al., 1998; Hennessy and Kilty, 2001). However, studies examining the effectiveness of explosive power have endeavoured to compare its relationship with a single sprint (Dowson et al., 1998; Hennessy and Kilty, 2001), neglecting the opportunity to compare explosive power with brief and prolonged RSA.
Consequently, the aim of the current study was twofold: (1) to examine the relationship between muscular leg strength and brief and prolonged RSA using a multi-joint strength measure (3RM squat), and (2) to establish if explosive power was more accurate in determining brief and prolonged RSA than muscular strength.
This study hoped to further an already extensively researched area of sports physiology, by clarifying the physiological determinants of brief and prolonged RSA. Once achieved, coaches and athletes could be informed of these physiological predictors, so they can be incorporated into highly effective training programmes specifically designed for team-sport athletes.