The effect of age-related differences in body size and composition on cardiovascular determinants of VO₂max

Background.A reduction in maximal stroke volume (SV_max) and total blood volume (TBV) has been hypothesized to contribute to the decline in maximal oxygen uptake (VO₂max) with healthy aging. However, these variables have rarely been collected simultaneously in a board age range to support or refute this hypothesis. It is also unclear to what extent scaling size-related cardiovascular determinants of VO₂max affects the interpretation of age-related differences.Methods.A retrospective analysis of VO₂max, maximal cardiac output (Q_Cmax), TBV, and body composition including fat-free mass (FFM) in 95 (51% M) healthy adults ranging from 19-86 years.Results.Absolute and indexed VO₂max, Q _Cmax, and maximal heart rate decreased in both sexes with age (p ≤. 031). SV_max declined with age when scaled to total body mass or body surface area (p ≤. 047) but not when expressed in absolute levels (p =. 120) or relative to FFM (p =. 464). Absolute and indexed TBVs (mL/kg; mL/m ²) were not significantly affected by age but increased with age in both sexes when scaled to FFM (p ≤. 013). A lower arteriovenous oxygen difference (a-vO₂diff) contributed to the reduction in VO ₂max with age in treadmill exercisers (p =. 004) but not in the entire cohort (p =. 128).Conclusion.These results suggest (a) a reduction in absolute SV_max, and TBV do not contribute substantially to the age-related reduction in VO₂max, which instead results from a smaller Q_Cmax due to a lower maximal heart rate, and (b) body composition scaling methods should be used to accurately describe the effect of aging on physical function and cardiovascular variables.