High-intensity interval training (HIT) describes physical exercise that is characterized by brief, intermittent bursts
of vigorous activity, interspersed by periods of rest or low-intensity exercise. HIT is infinitely variable with the specific physiological adaptations induced by this form of training determined by a myriad of factors including the
precise nature of the exercise stimulus (i.e. the intensity, duration and number of intervals performed, as well as the duration and activity patterns during recovery). When compared on a matched-work basis or when estimated energy expenditure is equivalent, HIT can serve as an effective alternate to traditional endurance training, inducing similar or even superior changes in a range of physiological, performance and health-related markers in both healthy individuals and diseased populations (Wisloff et al. 2007; Tjonna et al. 2009; Hwang et al. 2011). Less is known regarding the effects of low-volume HIT, but growing evidence suggests this type of training stimulates physiological remodelling comparable with moderate-intensity continuous training despite a sub- stantially lower time commitment and reduced total exercise volume (Gibala & McGee 2008). These findings are important from a public health perspective, given that ‘lack of time’ remains one of the most commonly cited barriers to regular exercise participation (Stutts 2002; Trost et al. 2002; Kimm et al. 2006). Moreover, recent evidence suggests that HIT is perceived to be more enjoyable than moderate-intensity continuous exercise (Bartlett et al. 2011). Here we review some of the mechanisms responsible for improved skeletal muscle metabolic control and changes in cardiovascular function in response to low-volume HIT, as well as the potential health-related implications for patients with chronic diseases including type 2 diabetes and cardiovascular disease. We also speculate on the practical application of low-volume HIT for elite performance. Although it is recognized that the underlying mechanisms are probably different compared with less-trained subjects (Iaia & Bangsbo 2010), responses in elite athletes may help our understanding of why low-volume HIT is such a potent exercise stimulus.