Cerebral hemodynamic reactions to low-intensity physical exercise.

Cerebral hemodynamic reactions to light physical exercise increasing stepwise on a bicycle ergometer were studied in healthy young male subjects. Hemodynamic parameters were measured by transcranial Doppler ultrasonography from the middle cerebral artery (MCA) before the start of the study and during the last few seconds of each exercise step. Cerebral hemodynamic reactions to physical exercise were characterized by a significant increase in systolic blood flow rate in the middle cerebral artery only at exercise levels of about 0.25 W/kg body weight (90 rpm at 0 W/kg) with no further increase in the blood flow rate with increases in loading to 0.5 W/kg body weight. The mechanism stabilizing blood flow rate in the cerebral arteries as physical exercise increased and, thus, the mechanism of cerebral circulatory autoregulation consisted of a arterial pressure-dependent increase in regional cerebral vascular resistance. The threshold at which the cerebral blood flow rate autoregulatory mechanism was triggered in normal subjects corresponded to a loading of about 0.25 W/kg and a systolic arterial pressure of about 140-145 mmHg.