Influence of sex and heart size on cardiovascular adaptations to 2 years of endurance exercise training in sedentary middle‐aged adults

Abstract Sedentary ageing is linked to low cardiorespiratory fitness and the development of a small, stiff heart – risk factors for heart failure. Endurance exercise training reverses the effects of sedentary ageing on the heart when started in middle age; however, blunted training responses of females have been reported. Differences in baseline cardiac size or exercise‐induced cardiac remodelling may underly sex differences in trainability. Therefore, we investigated whether sex and left ventricular end‐diastolic volume indexed to body surface area (LV EDVi) influence the cardiovascular response to endurance training. Twenty‐eight sedentary adults [15 females; age: 54 ± 5 years, peak oxygen uptake (): 28.8 ± 4.8 mL min −1 kg −1 ) completed 2 years of training, with cardiorespiratory fitness and LV EDVi assessed following 10 months of progressive training and an additional 14 months of maintenance training. The increase in peak (sex × time: P < 0.001) of females after 2 years (∆ = 0.27 ± 0.14 L min −1 ) was ∼50% of the increase of males (∆ = 0.53 ± 0.20 L min −1 ), resulting from smaller increases in peak cardiac output (sex × time: P = 0.005) and stroke volume (sex × time: P = 0.013). However, LV EDVi at rest, an index of exercise‐induced cardiac remodelling, increased during the progressive training phase (main effect: P < 0.001) independent of sex (sex × time: P = 0.888) despite females having smaller EDVi throughout the study (main effect: P = 0.004). Males ( r = −0.650, P = 0.016) and females ( r = −0.776, P < 0.001) with the smallest initial resting LV EDVi experienced the greatest increase in EDVi with training. Overall, structured endurance exercise training in middle‐aged females resulted in blunted increases in cardiorespiratory fitness compared to males despite both sexes experiencing similar degrees of cardiac remodeling. image Key points Endurance exercise training reverses the effects of sedentary ageing on the cardiovascular system if started in middle age, but the response to training could be modified by sex and baseline cardiac size and function We observed blunted increases in cardiorespiratory fitness of middle‐aged females compared to males with 2 years of endurance training, which were attributable to attenuated increases in peak stroke volume and cardiac output in females Both males and females experienced similar degrees of exercise‐induced cardiac remodelling, with people with the smallest hearts experiencing the greatest increase in left ventricular end‐diastolic volume index for each sex Our data demonstrate that the improvement in cardiorespiratory fitness with endurance exercise training is influenced by sex, but that the degree of cardiac remodelling with training in previously sedentary adults is not different between sexes, nor impaired by having a smaller pre‐training left ventricular end‐diastolic volume