Abstract Body (Do not enter title and authors here): Background: Sedentary aging is linked to low cardiorespiratory fitness and poor cardiovascular health. People with smaller left ventricles, particularly females, are more likely to have low fitness levels, which is an important risk factor for developing heart failure. Endurance exercise training can reverse the effects of sedentary aging in middle age, but it remains to be determined whether the cardiovascular adaptations to training are influenced by initial heart size and sex.
Methods: Twenty-eight sedentary adults [15 females; age: 54±5 yr, peak oxygen uptake (VO₂): 28.8±4.8 mL/min/kg] completed 2 years of endurance exercise training, with changes in left ventricular end-diastolic volume indexed to body surface area (LV EDVi) and cardiorespiratory fitness assessed following 10 months of progressive training and an additional 14 months of maintenance training.
Results: Despite baseline sex differences in LV EDVi at rest (male: 53.3±8.4 vs. female: 46.3±8.4 mL/m²; main effect: p=0.004), both male (Δ = 7.7±6.6 mL/m²) and female (Δ = 6.6±7.5 mL/m²) participants experienced similar increases in EDVi with 2 years of training (main effect of time: p<0.001). Male (r=-0.650, p=0.016) and female (r=-0.776, p<0.001) participants with the smallest initial resting LV EDVi experienced the greatest increase in EDVi with training (Figure), suggesting the greatest cardiac remodeling occurred in individuals with the smallest LV on baseline testing. The increase in peak VO₂ (sex × time: p<0.001) of female participants after 2 years (Δ = 0.26±0.14 L/min) was ~50% of the increase observed in male participants (Δ = 0.53±0.20 L/min), which was a consequence of smaller increases in peak stroke volume (sex × time interaction: p=0.013) and cardiac output (sex × time: p=0.005). The changes in arteriovenous O₂ difference at peak exercise with training did not interact with the effect of sex (sex × time: p=0.129). Pre-training LV EDVi was not associated with the increase in peak VO₂ with training (r=0.263, p=0.176).
Conclusion: Two years of structured endurance exercise training in middle age resulted in similar degrees of cardiac remodeling for both sexes; however, female participants still had blunted increases in cardiorespiratory fitness compared to male participants. Critically, the magnitude of improvement in cardiorespiratory fitness with endurance exercise training was not impaired in previously sedentary adults who had the smallest starting LV EDVi.