Reduced cardiac workload and enhanced oxygen extraction during maximal exercise in recreational endurance runners

BACKGROUND: This study assessed cardiac performance in response to maximal physiological stress in recreational long-distance runners. METHODS: In this cross-sectional observational study, 44 male recreational long-distance runners (age 32.6±8.8 years; body mass index 23.4±2.2 kg/m²) and 41 age-matched and sex-matched untrained controls performed a maximal cardiopulmonary exercise test on a cycle ergometer. Gas exchange and haemodynamic (bioreactance) measurements were assessed simultaneously. Cardiac power output (CPO), an integrative index of cardiac performance, was calculated from cardiac output and mean arterial pressure. Oxygen extraction was expressed as the arterial-venous oxygen difference (a-vO₂ diff). RESULTS: Runners achieved significantly higher maximal oxygen consumption than controls (53.2±6.8 vs 38.7±8.2 mL·kg⁻¹·min⁻¹, p<0.01) and higher peak work rate (276±31 vs 231±60 W, p<0.01). Despite superior aerobic capacity, runners demonstrated lower indices of cardiac performance at maximal exercise, including CPO (5.01±1.00 vs 5.64±1.46 W, p=0.03), cardiac output (18.7±3.0 vs 22.6±4.4 L·min⁻¹, p<0.01) and stroke volume (109±21 vs 126±28 mL·beat⁻¹, p=0.04). In contrast, a-vO₂ diff was approximately 30% higher in runners (21.6±3.7 vs 15.9±4.5 mL O₂·100 mL⁻¹ blood, p<0.01). CONCLUSIONS: Long-distance runners demonstrate higher oxygen consumption and oxygen extraction but lower haemodynamic response to maximal exercise stress test. These findings may suggest a potential cardioprotective role of endurance training characterised by reduced cardiac workload during maximal physiological stress.