Hit Training - Mechanisms of Adaptation - Prof. Gibala

Invited Session at ECSS Vienna 2016 "HIT training - Mechanisms and applicability"

Hit Training - Mechanisms of Adaptation
Gibala, M.
McMaster University

Interval exercise refers to the basic pattern of alternating periods of more intense effort with period of less intense effort, or complete
rest, within a single training session. Owing to the wide variety of terms used to describe this basic type of exercise, a classification
scheme was recently proposed to delineate “high intensity interval training” (HIIT) from “sprint interval training” (SIT) (1). HIIT
generally refers to submaximal exercise protocols in which the workload elicits a relative intensity corresponding to ≥80% of
peak heart rate. SIT describes protocols in which the intensity corresponds to ≥100% of the workload that elicits maximal
oxygen uptake (VO2max). Dating back several decades, numerous studies have examined physiological adaptations to HIIT and
traditional moderate-intensity continuous training (MICT), matched for total work or energy expenditure. While these have yielded
equivocal results, several recent systematic reviews and meta-analyses have concluded that HIIT elicits superior physiological
adaptations in both average healthy individuals and people with lifestyle-induced cardiometabolic disease (1-3). Research over the
last decade in particular has shed new light on the potency of low-volume interval training, which involves a relatively small total
amount of exercise, to elicit physiological adaptations that are comparable to MICT in a time-efficient manner (4). Studies that have
directly compared MICT to low-volume HIIT or SIT protocols have reported similar improvements in markers of aerobic energy
metabolism, as well as clinical indices of health status, despite large differences in total exercise and training time commitment.
Recent evidence supports the general contention that exercise intensity is more important than duration for exercise training-induced
increases in cardiorespiratory fitness (5). In contrast, the specific roles of intensity, duration and volume on aspects of
exercise-induced skeletal muscle remodelling, in particular mitochondrial biogenesis, are equivocal (6). Recent work suggests the
potential for SIT to promote greater and faster mitochondrial adaptations in human skeletal muscle than does HIIT or MICT despite a
much lower training volume (7). It was also reported in humans that muscle fibre-type specific responses to SIT were strikingly similar
to MICT despite lower training volume (8).
(1) Weston KS, et al. Br J Sports Med. 48:1227-1234, 2014.
(2) Bacon AP, et al. PLoS One. 8:e73182, 2013.
(3) Milanović Z, et al. Sports Med. 45:1469-1481, 2015.
(4) Gibala MJ, et al. J Physiol. 590:1077-1084, 2012.
(5) Ross R, et al. Mayo Clin Proc. 90:1506-1514, 2015.
(6) Bishop DJ, et al. Biochim Biophys Acta. 1840:1266-1275, 2014.
(7) Granata C et al. FASEB J. 2015 Nov 16.
(8) Scribbons B et al. PLoS One. 9:e98119, 2014.