Sex and age interaction in fundamental circulatory volumetric variables at peak working capacity

BACKGROUND: Whether the fundamental hematological and cardiac variables determining cardiorespiratory fitness and their intrinsic relationships are modulated by major constitutional factors, such as sex and age remains unresolved. METHODS: Transthoracic echocardiography, central hemodynamics and pulmonary oxygen (O(2)) uptake were assessed in controlled conditions during submaximal and peak exercise (cycle ergometry) in 85 healthy young (20–44 year) and older (50–77) women and men matched by age-status and moderate-to-vigorous physical activity (MVPA) levels. Main outcomes such as peak left ventricular end-diastolic volume (LVEDV(peak)), stroke volume (SV(peak)), cardiac output (Q(peak)) and O(2) uptake (VO(2peak)), as well as blood volume (BV), BV–LVEDV(peak) and LVEDV(peak)–SV(peak) relationships were determined with established methods. RESULTS: All individuals were non-smokers and non-obese, and MVPA levels were similar between sex and age groups (P ≥ 0.140). BV per kg of body weight did not differ between sexes (P ≥ 0.118), but was reduced with older age in men (P = 0.018). Key cardiac parameters normalized by body size (LVEDV(peak), SV(peak), Q(peak)) were decreased in women compared with men irrespective of age (P ≤ 0.046). Older age per se curtailed Q(peak) (P ≤ 0.022) due to lower heart rate (P < 0.001). In parallel, VO(2peak) was reduced with older age in both sexes (P < 0.001). The analysis of fundamental circulatory relationships revealed that older women require a higher BV for a given LVEDV(peak) than older men (P = 0.024). CONCLUSIONS: Sex and age interact on the crucial circulatory relationship between total circulating BV and peak cardiac filling, with older women necessitating more BV to fill the exercising heart than age- and physical activity-matched men. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13293-021-00409-9.