Sex dimorphism in cardiac and aerobic capacities: The influence of body composition

Abstract

ObjectiveThe contribution of body composition to sex differences in strong prognostic cardiorespiratory variables remains unresolved. This study aimed to elucidate whether body composition determines sex differences in cardiac and oxygen (O2) uptake responses to incremental exercise.MethodsHealthy, moderately active women and men (n = 60, age = 60.7 [12.3] years) matched by age and cardiorespiratory fitness were included. Body composition was determined via dual‐energy x‐ray absorptiometry. Transthoracic echocardiography and O2 uptake were assessed at rest and throughout incremental exercise with established methods. Major cardiac and pulmonary outcomes were normalized by body surface area (BSA), total lean body mass (LBM), or leg LBM.ResultsWomen presented with smaller anthropometrical indices (height, weight, BSA) and LBM compared with men (p < 0.001). Peak exercise cardiac dimensions and output (i.e., peak cardiac outout [Qpeak]), commonly normalized by BSA, were reduced in women relative to men (p ≤ 0.019). Cardiac sex differences were abolished after normalization by total or leg LBM (p ≥ 0.115). Strong linear relationships of total and leg LBM with Qpeak and peak oxygen uptake were detected exclusively in women (r ≥ 0.53, p ≤ 0.003), independent of body fat percentage.ConclusionsTotal and leg LBM stand out as strong independent determinants of cardiac and aerobic capacities in women, regardless of body fat percentage, relationships that are not present in age‐ and fitness‐matched men.

Lean body mass and the cardiovascular system constitute a female-specific relationship

“…At first sight, a thick and strong myocardial wall in the LV might facilitate cardiac output. In this regard, we recently found a close link between LBM and peak cardiac output in women (9). Given that most LBM is composed of muscular tissue and women have a tendency for LV concentric hypertrophy (12,21,22), the potential direct association between the amount of skeletal and cardiac muscle in the female body is an obvious initial hypothesis.…”

“…LBM was considered to represent the active mass of the human body, concurring the classic term "protoplasm," referring to the living substance of the body (11). LBM, in which the predominant tissue is skeletal muscle (12), is tightly associated with essential body functions and metabolic outcomes (9,(13)(14)(15). In a recent study, sex differences in cardiac output and peak exercise oxygen consumption were nulled when adjusted by LBM instead of typical body size parameters (9).…”

“…Consistent with the intertwined nature of biology, body composition is not merely an outcome. Although the extensive and sex-specific impact of body fat on health is firmly established ( 8 ), facets of LBM in human physiology might be on the brink of discovery ( 9 ).…”

“…LBM, in which the predominant tissue is skeletal muscle ( 12 ), is tightly associated with essential body functions and metabolic outcomes ( 9 , 13 – 15 ). In a recent study, sex differences in cardiac output and peak exercise oxygen consumption were nulled when adjusted by LBM instead of typical body size parameters ( 9 ). Unexpectedly, strong relationships of LBM with cardiac and aerobic capacities were exclusively found in women, whereas none were observed in men ( 9 ).…”

Heart rate and gas exchange dynamic responses to multiple brief exercise bouts (MBEB) in early‐ and late‐pubertal boys and girls

“…We did observe larger V̇O 2 , V̇CO 2 , and V̇E costs of MBEB in females compared to males (n.b., there was no sex × pubertal stage interaction). In the case of V̇O 2 , it has been challenging to directly compare oxidative capacity in response to exercise between women and men due to factors such as differences in body composition, (Diaz‐Canestro et al, 2021 ) blood volume, (Diaz‐Canestro et al, 2022 ) distribution of muscle fiber types, (Fournier et al, 2022 ) and gauging overall levels of conditioning. Men may demonstrate greater V̇O 2 responsiveness to exercise training than do women, (Diaz‐Canestro & Montero, 2019 ; Montero et al, 2018 ) suggest that even though muscle mass is smaller in women, mitochondrial volume is greater, perhaps explaining our finding of great V̇O 2 costs when normalized to the work performed.…”