Skeletal muscle phosphagen and lactate concentrations in ischaemic dynamic exercise

Five young males performed dynamic, submaximal contractions to exhaustion with the quadriceps muscle under arterial occlusion. The work load was 14.7 Watt (W). After 10 min rest with intact arterial circulation, the subjects commenced another bout to exhaustion; this process was repeated until a total of 10--16 bouts had been performed. Muscle biopsies were obtained immediately after the second, fifth, eighth, and last bout as well as 30 min after the last bout. The concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), lactate, and glycogen were measured in each sample and some material underwent histochemical analysis. Muscle lactate was highest following the second work bout [22.9 mmol/kg wet weight (ww)] and gradually declined to 7.0 mmol/kg ww by the end of the last bout. CP level was low in all postexercise samples with the exception of a remarkably high CP (11.7 mmol/kg ww) after the last bout. Glycogen utilization tended to parallel muscle lactate levels, the rate of depletion being most rapid initially. Histochemical staining for glycogen depletion revealed that both type I and II fibres were low in glycogen, although type I was depleted most uniformly. In the first work bouts the high lactate and low CP levels in the total muscle could be responsible for the fatigue; none of these factors seem adequate to explain the development of the fatigue experienced in the later work bouts. It is concluded that muscle fatigue in this type of exercise is not related to substrate depletion or accumulation of metabolites, further that the fibre recruitment pattern is determined by the type and relative severity of performed work rather than local metabolic factors.