Muscle Metabolites during Submaximal and Maximal Exercise in Man

Abstract

Methods are described for the determination of ATP, CP, Pi, glycogen, G-6-P, and lactate concentrations in muscle specimens (15 mg) obtained with a needle biopsy technique. Muscle biopsy specimens were obtained in two materials (n = 13; maximal oxygen uptake (max V˙o₂) 61 ml × min⁻³ × kg⁻¹ and n = 15; average max V˙o₂ 48 ml × min⁻¹ × kg⁻¹), at submaxi mal (55–95 per cent of max V˙o₂). and at short time exhaustive work levels. A depletion of the ATP and CP stores in relation to the relative work load was observed while the muscle lactate concentration increased faster at higher work loads concomitant with a tendency to an increased glycolysis. The ATP and CP stores (the phosphagens) could maximally account for an alactacid anaerobic energy output equivalent to 1.2–1.3 liters of oxygen. The lactacid anaerobic energy output, however, seemed to start when the phosphagens were lowered to approximately 70% of the basic values which occurred during steady-state work at work loads in excess of 50% of maximal oxygen uptake.