Due to the varied nature of football and more specifically, the physical duels associated with defensive positions, power was identified a crucial component of an elite defender (Hoff, 2005). Power, can be further understood as the ability to reach maximal velocity in the shortest amount of time (Cormie, McGuigan, and Newton, 2011).
Physiologically, power is highly dependent on sarcomere position, the largest amount of potential is available when optimal overlap between actin and myosin filaments is achieved; this is because at this point active tension is at its greatest, enabling muscles to contract with peak velocity (Gordon, Huxley, and Julian, 1966).
When tested, elite level players demonstrated superior levels of power when compared with sub-elite, supporting the notion that it’s an important factor in football fitness (Le Gall et al. , 2010). Although the majority of a football match is spent working at low speeds, crucial moments in the game are more commonly defined by short, high speed intervals (Sporis et al. , 2009; Reilly, Bangsbo, and Franks, 2000). Thus, sprint speed was deemed an import attribute for an established performer to possess.
Physiologically, speed is commonly associated with power and also depends on optimal contractions between actin and myosin filaments; however, research instils that the relationship is not completely linear and suggests sprint speed is also largely dependent bio-mechanics and motor unit efficiency (Gordon, Huxley, and Julian, 1966; Tonnessen et al. , 2011). Whilst sprint speed can be associated with power to some extent, due to some variability, it is apparent that both power and sprint speed need to be considered individually.
When tested, elite players demonstrated superior levels of acceleration and prolonged sprint speed, when compared with sub-elite players, supporting the notion that it’s an important attribute to possess (Little and Williams, 2005). As extended periods of a football match are spent working at relatively intensities, cardiovascular fitness can be considered an important component in football fitness (Bennike, Wikman, and Ottesen, 2014; Stolen et al. , 2005).
Furthermore, Russell and Kingsley (2011) explain, fatigue is highly debilitating to football performance, primarily because of the effect it has on skill acquisition. Thus, cardiovascular fitness can be considered highly important when aiming to maintain good performance. The onset of fatigue is said to negatively affect the body in two ways, one of which is lactate accumulation, which occurs when the body can no longer utilise oxygen to process pyruvate and results in the production of excess lactate; the second is heat accumulation (i. e.
hypeI~hermia), which can reduce enzyme activity (Berg, Tymoczko, and Stryer, 2002). Both lactate accumulation and excessive levels of heat have been shown to negatively impact the mechanical efficiency of cellular respiration, which limits the body’s available energy, thus, negatively impacting performance (Shephard and Astrand, 1993). Elite athletes have been shown to facilitate superior levels of cardiovascular fitness when compared with sub-elite performers, supporting the notion that it is an important component in football fitness (Ingebrigtsen et al.
, 2012). The relevance of body composition in sports performance is widely appreciated, specifically, for its capacity to illuminate a player’s physical status and provide a relevant indicator of their performance potential (Leedy, Ismail, Kessler, & Christian, 1965). Body composition has shown a considerable association with aerobic capacity and energy expenditure; when excessive, body fat can be considered a dead weight and ultimately negatively impacts a player’s capacity to perform (Reilly, 1996).
In addition, lean muscle mass and a good strength-to-weight ratio has been associated with superior sports performance (Gabbett, 2005). Miller et al. (2011) found, elite players would generally maintain lower levels of body fat throughout the season, supporting the notion that low body fat levels are associated with superior performance.