Intensity vs Volume: What Actually Builds Endurance? Exercise science finally gives us a clear answer 👇 Here’s what a large science-backed meta-analysis found: 1. Training intensity drives mitochondrial growth Higher intensity training led to up to 3.9x greater increases in mitochondrial content compared to lower intensity work. 2. Sprint interval training punches above its weight Short, intense sessions produced stronger mitochondrial adaptations than longer endurance sessions. 3. Volume matters, but less than you think More sessions help, but gains plateau faster than with increases in intensity. 4. Capillarization improves with consistency Capillary growth increases over time, especially after 8 weeks, regardless of training style. 5. Untrained individuals adapt faster Beginners see larger improvements than well trained athletes due to higher trainability. 6. Benefits apply across ages and health status Young, old, healthy, and clinical populations all showed positive adaptations. If time is limited, intensity delivers the biggest return. Train smart, not just long.