Local Metabolites and the Circulatory Adjustments to Exercise

The responses of the circulatory system to trapped metabolites from working muscles following varied amounts of exercise was studied. Four male subjects exercised on a friction type bicycle at work loads of 900 and 2,100 kg-m/min. for periods of time ranging from 1/2 to 10 min. Recovery from the exercise was permitted with uninterrupted lower leg circulation at one time and with leg circulation occluded during the first two minutes of recovery at another time. When the circulation to the lower limbs was occluded during recovery from exercise, systolic and diastolic blood pressures were always elevated above those found when there was uninterrupted circulation following exercise. When the heart rate was below 140 beats/min., occluding the circulation at the end of exercise always resulted in suddenly decreased heart rates. Occluding the circulation during recovery when rates were above 140 beats/min. prevented this sudden fall in heart rate levels. When circulation was restored to the legs, the systolic and diastolic blood pressures, in all cases, suddenly decreased approximately 60 mm Hg. Heart rate responses were dependent upon the heart rate level at the time the occluding cuffs were released. When the heart rate was less than 110 beats/min. the rate suddenly increased but when the heart rate was above 110 beats/min. there was no change. There were indications that local exercise metabolites could elicit reflexive blood pressure increases following both light and heavy work loads. The heart rate response to exercise appears to be related to factors such as the amount of metabolites trapped, and is modified by factors such as sudden blood pressure changes relative to the heart rate level.