Comparison of correlation between cardiorespiratory endurance (VO₂ max) and autonomic function test parameters in athletes and sedentary individuals

Abstract

Background and Study Aim. Maximal oxygen uptake (VO₂max) is considered the gold standard measure of aerobic capacity and reflects integrated cardiovascular, respiratory, and muscular adaptations to endurance training. Regular physical training is associated with enhanced parasympathetic tone and reduced sympathetic activity. Despite the use of autonomic function tests for evaluating cardiovascular autonomic regulation, the relationship between VO₂max and autonomic function test parameters remains a subject of practical interest. The study aim was to evaluate the relationship between VO₂max and autonomic function test parameters in athletes and sedentary individuals aged 18–25 years.

Materials and Methods. This cross-sectional comparative study included 80 healthy male volunteers divided into athletes (n = 40) and sedentary individuals (n = 40). VO₂max was directly measured using a cycle ergometer ramp protocol with incremental workload (10 W/min) and breath-by-breath gas analysis. Autonomic function was assessed using parasympathetic tests: Valsalva ratio, E:I ratio (deep breathing), and 30:15 ratio, and sympathetic tests: blood pressure response to standing and the isometric handgrip test (IHGT). Pearson correlation coefficient was used to evaluate associations between VO₂max and AFT parameters.

Results. Mean VO₂max was 27.47 ± 8.96 mL/kg/min in athletes and 26.06 ± 9.10 mL/kg/min in sedentary individuals. In all subjects (n = 80), correlations between VO₂max and AFT parameters were weak and statistically non-significant: Valsalva ratio (r = 0.067, p = 0.549), E:I ratio (r = −0.114, p = 0.313), IHGT response (r = −0.073, p = 0.516), fall in systolic BP on standing (r = −0.035, p = 0.753), and 30:15 ratio (r = 0.100, p = 0.375). In athletes, VO₂max showed a weak negative correlation with the E:I ratio (r = −0.274, p = 0.087) and IHGT response (r = −0.234, p = 0.145), although these were not statistically significant. Similar non-significant findings were observed in sedentary individuals.

Conclusions. VO₂max demonstrated no significant correlation with conventional autonomic reflex parameters in healthy young adults. This suggests that aerobic capacity and resting autonomic reflex function may represent relatively independent physiological domains.