Zone 2 cardio is the most underrated training tool for longevity

Zone 2 training — exercising at an intensity where you can still hold a conversation — builds mitochondrial density and metabolic efficiency in a way that higher-intensity exercise cannot. Research by Iñigo San Millán at the University of Colorado found that elite endurance athletes spend roughly 80% of their training time in Zone 2. For non-athletes, regular Zone 2 sessions improve insulin sensitivity, cardiovascular efficiency, and fat oxidation — and may be more predictive of long-term health outcomes than any other single exercise variable.

Source: San Millán & Brooks, Frontiers in Physiology (2018)