Leg blood flow during submaximal cycle ergometry is not reduced in healthy older normally active men

The purpose of the present study was to test the hypothesis that leg blood flow responses during submaximal cycle ergometry are reduced with age in healthy normally active men. Eleven younger (20-25 yr) and eight older (62-73 yr) normotensive, nonendurance-trained men performed both graded and constant-load bouts of leg cycling at the same absolute and relative [% of peak O-2 consumption ((V)over dotO(2) (peak))] exercise intensities while leg blood flow ( femoral vein thermodilution), mean arterial pressure ( MAP; radial artery), cardiac output ( acetylene rebreathing), blood O-2 content, and plasma catecholamines were measured. Leg blood flow responses at the same absolute submaximal power outputs (20-100 W) and at a fixed systemic O-2 demand (1.1 l/min) did not differ between groups ( P = 0.14-0.19), despite lower absolute levels of cardiac output in the older men (P < 0.05). MAP at the same absolute power outputs was 8-12 mmHg higher (P < 0.05) in the older men, but calculated leg vascular conductance responses ( leg blood flow/MAP) were identical in the two groups (P > 0.9). At the same relative intensity (60% (V)over dotO(2) (peak)), leg norepinephrine spillover rates were approximately twofold higher in the older men (P = 0.38). Exercise-induced increases in leg arterial-venous O-2 difference were identical between groups (P > 0.9) because both arterial and venous O-2 contents were lower in the older vs. younger men. These results suggest that the ability to augment active limb blood flow and O-2 extraction during submaximal large muscle mass exercise is not impaired but is well preserved with age in healthy men who are normally active.