In recent years, and partially driven through the Ancestral Health movement, high-intensity interval training (HIIT – in its various guises) has become the training mode de jour. But are we over-prescribing the dose of this training? A review of the current research literature on this suggests that high-intensity interval and sprint-type sessions induce a large amount of fatigue in the autonomic nervous system (ANS). Such ANS fatigue can have detrimental effects ranging from sleep disturbances through to HPA axis and stress-related issues. This session discusses the optimal dose for such forms of intense training.