Mitochondria biogenesis and interval training

Skeletal muscle is a highly malleable tissue, capable of pronounced metabolic and morphological adaptations in response to contractile activity (i.e. exercise). Repeated sessions of endurance exercise induce marked metabolic and structural adaptations within the skeletal muscle, one of the most striking being the pronounced increase in mitochondrial mass.

The magnitude of this change, or response to training, is dependent on the nature of the training programme. In order to increase the muscle oxidative capacities, continuous (CT) and interval training (IT) are both established exercise modalities used in the preparation of elite athletes as well as in the rehabilitation of patients with chronic diseases.

There is considerable debate as to which training program (CT vs. IT) will have a greater effect on aerobic performance and there are relatively few studies which have directly compared skeletal muscle metabolic adaptations to interval and continuous training.

Mitochondrial biogenesis is a complex process that involved the expression of a large number of genes encoded by both the nuclear and mitochondrial genome, and the molecular events coordinating these expressions within-cell training adaptations remains to be clarified.

The succession of on-transient phases that induce a repetition of metabolic changes is a possible mechanism responsible for the greater response to IT. The objective of this study was to quantify VO₂ fluctuations during intermittent exercise characterised by the same work:rest ratio, but different durations and identify which duration leads to the greatest fluctuations.

Ten participants performed an incremental test to exhaustion to determine peak work rate and oxygen uptake, and three 1-hour intermittent exercises alternating work period at 70% WR peak with passive recovery period of different 1:1 work:recovery duty-cycles (30s:30s, 60s:60s, 120s:120s).
VO₂ response analysis revealed differences in the fluctuations across the intermittent conditions despite an identical total energy expenditure. The sum of the cycle’s nadir-to-peak VO₂ differences and the oxygen fluctuation index (OFI) were both greater in the 60s:60s condition

The findings also demonstrated that the selection of the duty-cycle duration for submaximal intermittent exercise (70% of WRpeak) prescription is of
interest to produce high VO₂ fluctuations.

Publications
Combes, A., Dekerle, J., Bougault, V. & Daussin, F.N. (2016). Effect of work:rest cycle duration on VO2 Fluctuations during Intermittent Cycling. Journal of Sport Sciences. 1-7.

A. Combes, J. Dekerle, N. Webborn, P. Watt, V. Bougault, F.N. Daussin.. Metabolic fluctuations influence peroxisome proliferator-activated receptor gamma coactivator-1 alpha upstream signalling kinases in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol (September 2015).