> In this systematic review and meta-regression covering ~ 50 years of research data, we demonstrate that the magnitude of change in mitochondrial content, capillarization, and VO2 max to exercise training is largely determined by the initial fitness level. The ability to adapt to
exercise training is maintained throughout life irrespective
of sex and presence of disease. Larger training volumes (higher training frequency per week and larger number of training weeks) and higher training intensities (per hour of training, SIT > HIT > ET) are associated with greater
increases in mitochondrial content and VO2 max. Therefore, training load (volume x intensity) is a robust predictor of changes in mitochondrial content and VO2 max.
Increases in capillarization occur primarily in the early stages of exercise training (< 4 weeks) with ET, HIT, and SIT equally enhancing capillaries per fiber, while ET is
more effective in increasing capillary density (capillaries
per mm²) due to less pronounced muscle fiber hypertrophy.
A good summary: https://bannister.coach/mitochondria-and-exercise-how-differ...
Quoting the conclusion:
> In this systematic review and meta-regression covering ~ 50 years of research data, we demonstrate that the magnitude of change in mitochondrial content, capillarization, and VO2 max to exercise training is largely determined by the initial fitness level. The ability to adapt to exercise training is maintained throughout life irrespective of sex and presence of disease. Larger training volumes (higher training frequency per week and larger number of training weeks) and higher training intensities (per hour of training, SIT > HIT > ET) are associated with greater increases in mitochondrial content and VO2 max. Therefore, training load (volume x intensity) is a robust predictor of changes in mitochondrial content and VO2 max. Increases in capillarization occur primarily in the early stages of exercise training (< 4 weeks) with ET, HIT, and SIT equally enhancing capillaries per fiber, while ET is more effective in increasing capillary density (capillaries per mm²) due to less pronounced muscle fiber hypertrophy.