Forearm skin and muscle vascular responses to prolonged leg exercise in man.

To determine the cutaneous and resting skeletal muscle vascular responses to prolonged exercise, total forearm blood flow (FBF-plethysmography) (5 men) and forearm muscle blood flow (MBF-[125I]antipyrine clearance) (4 men) were measured throughout 55-60 min of bicycle exercise (600-750 kpm/min). Heart rate (HR) and esophageal temperature (Tes) were also measured throughout exercise. FBF showed only small changes during the first 10 min followed by progressive increments during the 10-40 min interval and smaller rises thereafter. For the full 60 min of exercise, there was an average increase in FBF of 8.26 ml/100 ml-min. MBF showed an initial fall with the onset of exercise (on the average from 3.84 to 2.13 ml/100 ml-min) which was sustained or fell further as exercise continued, indicating that increments in FBF were confined to skin. Much of the increase in FBF occurred despite essentially constant Tes. Results suggest that the progressive decrements in central venous pressure, stroke volume, and arterial pressure previously seen during prolonged exercise are due in part to progressive increments in cutaneous blood flow and volume.