Mitochondrial density is one of the key physiological adaptations distinguishing trained from untrained endurance athletes. Masters cyclists experience a natural decline in mitochondrial density that zone 2 training counteracts. Long low-intensity rides (2+ hours at VT1 or below) drive mitochondrial biogenesis via the PGC-1α signalling pathway — this is why Prof. Seiler, Inigo San Millán and the World Tour coaches insist on volume at low intensity. High-intensity work improves the efficiency of existing mitochondria; only low-intensity volume grows new ones.
RELATED TERMS