An elevated resting heart rate was observed to persist for a few hours after pre-study sports practice in our previous study. It is very important to determine whether this higher heart rate response had any effects on school students with morning classes. Therefore, this study investigated the physiological background of persistent elevation of the resting heart rate following pre-study sports practice. The subjects were five young men ranging in age from 23 to 30 years. They exercised for one hour on a bicycle ergometer at 55% t0= max between 8 am and 9 am. During and after the exercise, the heart rate, oxygen consumption, blood pressure, rectal temperature, plasma lactic acid, plasma sodium, plasma potassium, plasma chlorine, plasma glucose, percentage change in plasma volume (APV) , adolenarine, noradolenarine and aldosterone were measured from 8 am to 3 pm. A significant observation was that the higher resting heart rate persisted after exercise until 3 pm in comparison with that in the control study. The other measured items, however, did not show any significant changes, excluding APV. APV decreased at 9 am just after the exercise, then continued to increase until 3 pm. These results suggested that persistent elevation of the resting heart rate after pre-study sports practice was not caused by elevation of aerobic metabolism and/ or sympathicotonia. This study could not identify the physiological cause of the persistent elevation of the resting heart rate.
