Similar to traditional endurance or strength training, physiological adaptations to HIIT are highly dependent on the precise nature of the training stimulus, i.e., the frequency, intensity and volume of work performed. However, unlike the other two general categories of exercise training which primarily rely on either oxidative (endurance) or nonoxidative (strength) energy to fuel ATP provision, the bioenergetics of highintensity exercise can differ markedly depending on the duration and intensity of each interval, the number of intervals performed and the nature and duration of recovery between efforts (Ross & Leveritt, 2001). For example, during a single 30s allout maximal cycling effort, approximately 20% of total energy provision is derived from oxidative metabolism (Parolin et al., 1999). However, if the exercise bout is repeated three times with four min recovery between bouts, the majority of ATP provision during the final bout is derived from oxidative metabolism (Parolin et al.,