The purpose was to investigate time of day on responses to two types of exhaustive cycle ergometer tests. Sixteen males performed six exercise tests: three - constant power protocol and three - incremental protocol. The first test was a learning trial; the other tests were performed one in the morning and one in the afternoon. ANOVA revealed that O2 deficit and lactate were higher in the afternoon than the morning. Regardless of test type, time to exhaustion tended to be higher in the afternoon. VO2max was unaffected by the time of day and test type. These results confirmprevious reports of a time of day effect on anaerobic capacity, and support the contention that V02max is stable about a day.

The effects of moderate workload exercise at different pedal rates on circulatory and respiratory parameters were studied. Five subjects performed seven discontinuous constant-load cycle ergometer tests of 30 minutes duration at pedal rates of 40, 50, 60, 70, 80, 90 and 100 rpm. Oxygen uptake and carbon dioxide production were determined by standard open circuit spirometry, while heart rate was recorded by electrocardiograph. The CO₂ rebreathing procedure was administered during the exercise bout in order to determine cardiac output. Blood pressure was determined for each test, and total peripheral resistance was calculated. The findings indicate that progressive increases in pedal frequency during discontinuous constant-load cycle ergometry produce progressive increases in cardiovascular, respiratory and metabolic responses and a decrease in gross exercise mechanical efficiency. The results indicate that oxygen uptake, cardiac output, heart rate, ventilation and arterial-venous oxygen difference increases curvilinearly as pedal rate increases, possibly as a result of increases in recruitment of muscle fibers and/or muscle groups. These findings suggest that circulatory and respiratory responses are due to "central command" which sets the basic efferent response pattern. However, this effector pattern is modulated by afferent input originating from the legs during progressive increases in pedal rate.