Progressive fatigue that occurs during high-intensity intermittent exercise, characteristic of many team sports including football, has been typically ascribed to the depletion of
muscle glycogen, reductions in circulating blood glucose, hyperthermia, and the progressive loss of body fluids (Mohr, Krustrup, & Bangsbo, 2005). These factors are thought to result in a reduction in distances covered, and the number and intensity of sprints undertaken by players, towards the end of the second half of play (Mohr, Krustrup, & Bangsbo, 2003). Although the idea that the central nervous system (CNS) is involved in feelings of tiredness, lethargy, and mood disturbances is not new, evidence has accumulated over the past 20 years to support a significant role of the brain in the aetiology of fatigue during strenuous exercise. It is now acknowledged that the cause of fatigue is a complex phenomenon influenced by both events occurring in the periphery and the CNS (Meeusen & De Meirleir, 1995; Nybo & Secher, 2004).