Leg Blood Flow and V̇O₂ during Peak Cycle Exercise in Younger and Older Women

Purpose: To test the hypothesis that leg blood flow and leg O₂ extraction during peak exercise are reduced with age in healthy normally active women. Methods: Thirteen younger (20-27 yr) and 12 older (60-71 yr) nonendurance trained women performed graded upright leg cycling to maximum exertion (V̇O_2peak), while leg blood flow (femoral vein thermodilution), cardiac output (acetylene rebreathing), mean arterial pressure (MAP, radial artery), and blood O₂ contents were measured. Results: Peak leg V̇O₂ was 32% lower in the older versus younger women (0.81 ± 0.06 vs 1.18 ± 0.10 L·min^-1) and was correlated with peak systemic V̇O₂ (1.33 ± 0.1 vs 1.78 ± 0.1 L·min^-1) in both groups. Peak leg blood flow and estimated leg vascular conductance were 29% and 38% lower, respectively, in the older women (both P < 0.001). Peak leg blood flow and peak estimated cardiac output were correlated in the older (r² = 0.51, P = 0.02), but not younger (r² = 0.10, P = 0.35), group. Estimates of peak systemic and leg arterial-venous O₂ difference did not differ between groups (both P > 0.28). Conclusions: Reduced leg blood flow is a major contributor to the reduced peak systemic V̇O₂ observed in older nonendurance trained women. Diminished leg blood flow during peak exercise in older women, in turn, is due to both central (reduced cardiac output) and peripheral (reduced leg vascular conductance) limitations.