Background: We tested the hypothesis that the nonactive limb vasoconstriction evoked during large-muscle dynamic exercise becomes augmented with aging in humans.
Methods and results: Sixteen young control subjects (age, 26 +/- 1 year) and twelve older (65 +/- 1 year) healthy men with similar chronic physical activity levels were studied during supine leg cycling exercise. Both peak work load (1,100 +/- 60 versus 1,400 +/- 40 kpm/min) and peak O2 uptake (1.85 +/- 0.10 versus 2.38 +/- 0.07 l/min) were lower in the older men (p < 0.05). There were no differences in the two groups under conditions of quiet supine (basal) rest. During cycling for 5 minutes each at mild, moderate, and heavy submaximal intensities (approximately 45%, 65%, and 85% of peak O2 uptake), the increases in arterial blood pressure generally were similar in the young and older subjects; however, heart rate rose less in the older men (p < 0.05). Whole forearm blood flow (venous occlusion plethysmography) was lower and vascular resistance was higher (approximately 55-90%) in the older men at all loads (p < 0.05), but the steady-state forearm skin blood flow responses (laser Doppler velocimetry) were not different in the two groups. The increases in antecubital venous norepinephrine concentrations were greater in the older men at each work load (p < 0.05), although the plasma epinephrine responses were similar in the two groups. In other studies, 1) peak whole forearm reactive hyperemia and vascular conductance after sustained circulatory arrest (ischemia) were slightly (approximately 20%) but not significantly lower in the older men and 2) the forearm vasoconstrictor and plasma norepinephrine responses to a nonexercise sympathoexcitatory stimulus (limb immersion in ice water) tended to be blunted in the older men.
Conclusions: During brief, submaximal, large-muscle dynamic exercise, healthy older men demonstrate augmented forearm vasoconstriction that is probably caused by greater constriction of skeletal muscle resistance vessels; this appears to be mediated, at least in part, by increased sympathetic outflow. These altered sympathetic vasoconstrictor adjustments do not represent a nonspecific hyperresponsiveness to acute stress with human aging. Finally, the regulation of arterial blood pressure appears to be normal in these healthy older men.