Running employs aerobic energy system (produces energy from oxygen, fat and carbohydrate), which turns to anaerobic lactic acid energy system (higher percent of carbohydrate used in relation to oxygen) if running short distances at high speed. (personaltraining4u.net)
Aerobic energy systems training that allows for a general level of conditioning s the foundation for the other two energy systems. (pnorthfitness.com)
The alactic anaerobic energy system described above is the first system recruited for muscle contraction and can last for only about 10 seconds of intense exercise after which the lactic anaerobic and aerobic energy systems become the main contributors to ATP production. (shapesense.com)