Changes in ATP and Creatine Phosphate Storage in Skeletal Muscle of Rats trained at 900 and 7,600 Feet

Abstract

THE hydrolysis of ATP provides the energy source for muscular contraction. ATP is either stored in the muscle or produced by phosphorylation of ADP by creatine phosphate or glycolytic processes, or through oxidative processes in the mitochondria. The processes of adaptation which facilitate the glycolytic or oxidative production of ATP have been studied in trained and acutely exercised animals. After work has been done by the muscle, the oxidative¹ and glycolytic^2,3 capacities of its fibres increase. Christensen⁴ has shown that neither glycolysis nor oxidative processes take place during short anaerobic bursts of activity. The energy for such limited activities is provided by the hydrolysis of stored ATP and phosphorylation of ADP by creatine phosphate by the Lohman reaction. Previous exercise studies using endurance types of training have not shown any adaptation of either ATP or creatine phosphate^5–7, although electrical stimulation⁸ and dwelling at high altitude⁹ have produced increases in creatine phosphate.