Slow down your training to build a faster metabolic engine.
For a long time, I believed that cardiovascular conditioning required gasping for air at maximum heart rate during every session. However, examining cellular energetics highlighted the power of Zone 2 training (exercising at an intensity where blood lactate remains below 2.0\text{ mmol/L}). In this aerobic steady state, Type I slow-twitch muscle fibers rely almost exclusively on fat oxidation within mitochondrial matrices. High-intensity intervals, while valuable, recruit fast-twitch glycolytic fibers that flood the system with lactate and suppress mitochondrial biogenesis. Building a broad Zone 2 base expands mitochondrial density, improves resting insulin sensitivity, and increases fat-burning capacity.
Building an elite aerobic engine requires spending substantial time at an easy, conversational pace to develop your cellular infrastructure.
Do you incorporate dedicated low-intensity Zone 2 sessions into your weekly training split?
MBH/PS