From an energy-low signal to new mitochondria
AMPK is a cellular fuel gauge. When energy demand outstrips supply, ATP is consumed and AMP and ADP accumulate, raising the AMP-to-ATP ratio. AMPK senses this shift and becomes active, signaling that the cell is running low on energy. Endurance exercise is a strong physiological trigger because muscle burns ATP rapidly.
Once active, AMPK promotes the transcriptional coactivator PGC-1alpha, often described as a master regulator of mitochondrial biogenesis, the building of new mitochondria.
Why more mitochondria improve endurance
PGC-1alpha coordinates the expression of genes needed to assemble additional mitochondria, increasing the cell's capacity to produce ATP aerobically. Over repeated training, this is part of why trained muscle fatigues less at a given workload and uses fat more effectively for fuel.
Mitochondrial biogenesis is a gradual adaptation built over weeks of consistent stimulus, not an overnight change, and AMPK is one node in a larger network rather than a standalone switch. This is general educational information about exercise physiology, not medical advice.