EFFECTS OF PROLONGED EXERCISE AT A SIMILAR PERCENTAGE OF MAXIMAL OXYGEN-CONSUMPTION IN TRAINED AND UNTRAINED SUBJECTS

Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (% VO2max) as a normalising independent variable is valid despite significant differences in the absolute VO2max of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine VO2max and lactate threshold. The subjects were grouped as trained (T) if their VO2max exceeded 60 ml.kg-1.min-1, and untrained (UT) if their VO2max was less than 50 ml.kg-1.min-1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70% VO2max. The allocation of each exercise session (50% or 70% VO2max) was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (-10 min), just prior to the commencement of exercise (0 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+10 min) and analysed for concentrations of cortisol, [Na+], [K+], [Cl-], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (VO2) and related variables were measured at two time intervals (14-15 and 34-35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50% VO2max for heart rate (f(c)) and venous [la-]. At 70% VO2max, VO2 and ventilation (V(E)) for the T group and VO2, V(E) and carbon dioxide production for the UT group increased significantly with time and there was a significant interaction effect for f(c), [la-], [Hb] and [NH3]. The change in body mass at 50% and 70% VO2max was significantly greater in the T group. The present study found that when two groups of male subjects with different absolute VO2max exercised at a similar percentage of VO2max some effector responses were significantly different, questioning the validity of selecting % VO2max as a normalising independent variable.