Abstract
Endurance exercise is associated with increased life duration and improved life quality. Paradoxically, high exercise intensity is also associated with increased coronary artery calcification (CAC) and a small but significant increased risk of adverse cardiac events during exercise. The mechanisms underlying the development of CAC during prolonged high-intensity endurance exercise are unknown. This study aims to determine if there are differences in cardiovascular haemodynamic measures and heart rate variability (HRV) in individuals with (CAC(+)) and without CAC (CAC(-)). Hemodynamic measures from 56 healthy, middle-aged (median [interquartile range] 51 [43-58] years) individuals (41 men/15 women) participating in a 91 km [251.2 [217.2-271.6] min] leisure sport mountain bike race were included in this study. Twenty-five participants (20 men/5 women) were classified as CAC(+) based on coronary computed tomographic assessment. Haemodynamic measures and HRV were quantified at the top of the hardest hill (THH) during the last quarter of the race. At the top of THH, CAC(+) individuals had significantly higher systolic blood pressure (SBP) (235 [225-245] mmHg vs. 220 [193-238] mmHg, P = 0.008), higher diastolic blood pressure (DBP) (105 [95-110] mmHg vs. 95 [85-110] mmHg, P = 0.006), higher pulse pressure (130 [125-140] mmHg vs. 123 [110-130] mmHg, P = 0.039), higher mean rate pressure product (33,882 [30,872-35,053] bpm × mmHg vs. 31,028 [27,392-33,047] bpm × mmHg, P = 0.028), and larger increase in DBP from baseline (20 [20-30] mmHg vs. 10 [0-20] mmHg, P = 0.001), compared with CAC(-) individuals. Further, CAC(+) participants showed a significant reduction in the low-frequency component of HRV (HRV(LF)) (6.3 [2.4-11.5] ms(2) vs. 12.4 [6.8-20.2] ms(2), P = 0.044). In multivariable analysis, HRV(LF) was an independent predictor of the presence of CAC even after adjusting for established risk factors of atherosclerosis: age, sex, body mass index, maximum heart rate, V̇O2max , smoking, resting SBP and resting DBP. CAC(+) individuals had significant alterations in haemodynamic measures and HRV(LF) following prolonged high-intensity endurance exercise compared with individuals without CAC. HRV(LF) was an independent predictor of CAC, suggesting an adverse autonomic response to high-intensity endurance exercise in individuals with CAC.