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The influence of short-term high-altitude (HA) residence on intramuscular pH and skeletal muscle enzyme activity of sea-level (SL) residents was investigated. Vastus lateralis muscle samples were obtained by biopsy from rested subjects (n = 5) at SL (50 m) and on the 18th day of HA residence (4,300 m) for determination of glycogen phosphorylase, hexokinase, malate dehydrogenase, and total lactate dehydrogenase activities. A second group of subjects (n = 6) performed cycle exercise of the same absolute intensity (mean +/- SE = 195 +/- 5 W) at SL and on the 15th day of residence at HA. Before and immediately after exercise, vastus lateralis muscle samples were obtained for the determination of intramuscular pH, and venous blood was obtained for determination of lactate concentration. The first group of subjects showed no significant changes in skeletal muscle enzyme activity after 18 days at HA. The second group of subjects were instructed to exercise for exactly 30 min, and all but one could complete the entire bout at SL. However, at HA, none could continue 30 min, and time to exhaustion (mean +/- SE) was 11.9 +/- 1.6 min. Resting intramuscular pH was not significantly different after HA residence as compared to SL. The fall in intramuscular pH was less with exercise on day 15 at HA than during SL exercise. Likewise, the increase in blood lactate concentration with exercise at HA was less than at SL. These data indicate that, after 15-18 days of HA residence, limitations in exercise performance are not due to inordinate intramuscular acidosis or to changes in the activity of glycolytic and oxidative enzymes.

The purpose of this study was to examine the effect of intense interval training on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) levels at rest and after maximal exercise. Eight normal men, mean +/- SE = 24.2 +/- 4.3 years, trained 4 days X week-1 for a period of 8 weeks. Each training session consisted of eight maximal 30-s rides on a cycle ergometer, with 4 min active rest between rides . Prior to and after training the subjects performed a maximal 45-s ride on an isokinetic cycle ergometer at 90 rev X min-1 and a graded leg exercise test ( GLET ) to exhaustion on a cycle ergometer. Blood samples were obtained from an antecubital vein before, during and after the GLET only. Training elicited significant increases in the amount of work done during the 45-s ride (P less than 0.05), and also in maximal oxygen uptake (VO2 max: Pre = 4.01 +/- 0.13; Post = 4.29 +/- 0.07 1 X min-1; P less than 0.05) during exercise and total recovery VO2 (Pre = 19.14 +/- 0.09; Post = 21.45 +/- 0.10 1 X 30 min-1; P less than 0.05) after the GLET . After training blood lactate was higher, base excess lower and pH lower during and following the GLET (P less than 0.05 for all variables).(ABSTRACT TRUNCATED AT 250 WORDS)