[Effect of a 30-day period of hypokinesia on various physiologic and biochemical indicators during maximal physical...

Exercise tolerance of test subjects who remained bed rested (Group A) and who exercised while being supine (Group B) was measured before and after 30-day head-down tilt (-8 degrees). Special attention was given to the parameters that characterize energy supply of working muscles. The data obtained after 30-day bed rest did not reveal any changes in the Group B subjects and showed the following changes in the Group A subjects: maximum oxygen consumption decreased by 10.1% (p less than 0.05), the time within which the anaerobic metabolism threshold was attained decreased by 17.2% (p less than 0.05), and lactate concentration at the workload end decreased by 24.7%, while the pyruvate concentration and the lactate/pyruvate ratio remained unchanged. The results indicate that prolonged aerobic workload after 30-day bed rest seems to be limited by functional changes in oxygen transport rather than by the factors associated with changes in energy supply of working muscles.