REDUCED LEG BLOOD-FLOW DURING DYNAMIC EXERCISE IN OLDER ENDURANCE-TRAINED MEN

It is currently unclear whether aging alters the perfusion of active m uscles during large-muscle dynamic exercise in humans. To study this i ssue, direct measurements of leg blood flow (femoral vein thermodiluti on) and systemic arterial pressure during submaximal cycle ergometry ( 70, 140, and 210 W) were compared between six younger (Y; 22-30 yr) an d six older (O; 55-68 yr) chronically endurance-trained men. Whole bod y O-2 uptake, ventilation, and arterial and femoral venous samples for blood-gas, catecholamine, and lactate determinations were also obtain ed. Training duration (min/day), estimated leg muscle mass (dual-energ y X-ray absorptiometry; Y, 21.5 +/- 1.2 vs. O, 19.9 +/- 0.9 kg), and b lood hemoglobin concentration (Y, 14.9 +/- 0.4 vs. O, 14.7 +/- 0.2 g/d l) did not significantly differ (P > 0.05) between groups. Leg blood f low leg vascular conductance, and femoral venous O-2 saturation were s imilar to 20-30% lower in the older men at each work rate tall P < 0.0 5), despite similar levels of whole body O-2 uptake. At 210 W, leg nor epinephrine spillover rates and femoral venous lactate concentrations were more than twofold higher in the older men. Pulmonary ventilation was also higher in the older men at 140 (+24%) and 210 (+39%) W. These results indicate that leg blood flow and vascular conductance during cycle ergometer exercise are significantly lower in older endurance-tr ained men in comparison to their younger counterparts. The mechanisms responsible for this phenomenon and the extent to which they operate i n other groups of older subjects deserve further attention.