Summary • The purpose of interval training is to perform a greater amount of total work at a high exercise intensity. • A high intensity interval training session for an endurance athlete elicits near-maximal levels of cardiac output, relatively high levels of muscular recruitment as well as near-maximal metabolic rates and progressively increasing aerobic energy demands. • High intensity interval training in a variety of forms can elicit improvements in endurance performance in endurance athletes, and the mechanisms at play appear to be both central (cardiovascular) and peripheral (neuromuscular) in origin. • As central cardiovascular mechanisms appear to have the greater influence on endurance performance, performing intervals at intensities near V02max may be optimal (> 90%). • While interval training over a relatively short period (2-6 weeks) can be an effective means of acutely enhancing performance, too many high intensity interval training sessions without adequate recovery can lead to signs of overtraining, and as a general rule should be limited to 1-2 sessions per week. • Interval training for an endurance athlete is theoretically optimized when interval durations range from between 3-7 min, and each interval intensity is perceived as `hard`, with the last interval perceived as `very hard`. • Recovery bout duration and intensity should be sufficient to allow for the main purpose of interval training, which is to perform more high intensity work, and around 2 min of recovery appears to be optimal.
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