Oxidative metabolism and anaerobic glycolysis during repeated exercise

The purpose of the present study was to examine aerobic and muscle anaerobi c energy production during supramaximal repeated exercise. Eight subjects p erformed three 2-min bouts of cycling (EX1-EX3) at an intensity correspondi ng to about 125 % of VO2 max separated by 15 min of rest. Ventilatory varia bles were measured breath by breath during the exercise and a muscle biopsy was taken before and after each exercise bout. Blood samples were collecte d before and after each cycling period and during the recovery periods. Tot al work in the first 2 min bout of cycling, EX1, [46.3 +/- 2.1 KJ] was grea ter than in the second, EX2, (p < 0.01) and in the third, EX3, (p < 0.05). The ATP utilization [4.0 1.4 mmol.(kg dry weight)(-1), EX1] during the thre e exercise bouts was the same. The decrement in muscle phosphocreatine (PCr ) [46.8 +/- 8.5 mmol(kg dry weight)(-1), EX1] was also similar for the thre e exercise bouts. Muscle lactate accumulation was greater (p < 0.05) during EX1 compared to EX2 and EX3. The total oxygen consumption was the same for the three exercise bouts, but when it is corrected for the total work perf ormed, oxygen uptake during EX2 (153 +/- 9 ml.KJ(-1)) and EX3 (150 +/- 9 ml KJ-I) was higher (p < 0.01 and p < 0.05, respectively) than during EX1 (13 9 +/-: 8 ml.KJ(-1)). The present data suggest that oxidative metabolism doe s not compensate for the reduction of anaerobic glycolysis during repeated fatiguing exercise.