I assume this is asking which process produces energy in this case. Since the muscles are being deprived of oxygen that means that the ‘Krebs Cycle’ can not occur. In the absence of oxygen, pyruvate ferments into lactic acid, which produces small amounts of ATP which is where the athlete would get the energy. (Since only small amounts of atp are produced and lactic acid builds up, this is why we cant work our muscles too hard for too long!)
