Mølmen et al. 2025, Exercise training and mitochondrial and capillary growth meta-regression

A systematic review and meta-regression of 353 training studies (5,973 participants) found that endurance, high-intensity interval and sprint interval training all produce similar absolute gains in mitochondrial content (~23–27%), but sprint interval training is roughly 2–4 times more time-efficient per hour of exercise (approximately 2.3× vs HIT and 3.9× vs endurance training). Capillarisation improvements were greatest with endurance training and plateaued early (within four weeks), occurring primarily in untrained-to-moderately trained individuals; the magnitude of all adaptations was determined largely by initial fitness level. Cumulative training load (volume × intensity) was the best predictor of mitochondrial content and VO₂max gains. Strong evidence.