40 healthy male students were randomly assigned to either the exercise or control group. The latter was asked not to alter their common physical activity while the exercise group trained three times weekly on the bicycle ergometer for 15 minutes with a constant heart rate of 140bpm. At the beginning and after five weeks physiological data comprising cardiovascular and pulmonary responses at rest and under submaximal ergometric exercise were assessed. Additional data included psychological achievement tests, self reports of personality dimensions and frequency of physical complaints. Results indicated a marked increase in physical fitness for the training group improving the work load from 158 watt to 197 watt at constant heart rate. At rest and especially at submaximal work load there was an improvement of the economy of the cardiovascular and respiratory system. Contrary to these findings there were no changes or impairment in the psychological achievement tests, measuring concentration. Compared with the control group self reports of personality dimensions did not change except for a tendency to more extrovert behavior in the exercise group. Unexpectedly, the frequency of physical complaints did not decrease. The reason for this discrepancy is discussed.