Physiological adaptations to interval training and the role of exercise intensity.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing physiology literature without a systematic review methodology.
PubMed 27748956 · doi:10.1113/JP273196
What was done
This brief narrative review synthesized existing literature on how exercise intensity mediates physiological adaptations, focusing on aerobic energy metabolism. It compared high-intensity interval training (HIIT, near-maximal efforts) and sprint interval training (SIT, supramaximal efforts) with moderate-intensity continuous training (MICT).
What was found
The abstract reports no numerical values or effect sizes. Qualitatively, HIIT generally increases maximal oxygen uptake (VO2 max) to a greater extent than MICT when matched for training volume, whereas SIT and MICT yield similar increases in VO2 max despite lower exercise volume in SIT. For skeletal muscle, limited data suggest work-matched HIIT produces superior mitochondrial content gains compared to MICT within the same individual, while SIT increases mitochondrial content similarly to MICT with lower volume.
Why it matters
The review highlights exercise intensity as a key trigger for mitochondrial biogenesis and cardiorespiratory adaptations, showing that brief interval protocols can achieve metabolic improvements equivalent or superior to high-volume continuous endurance exercise.
Limits
As a narrative review, it lacks systematic search protocols, quantitative meta-analysis, and study count or sample size details in the abstract. The authors note limited available evidence on skeletal muscle capillary density, maximum stroke volume, cardiac output, and blood volume, as well as an incomplete understanding of interactions among intensity, duration, and frequency.
Cited by
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