Comparative Cross-Sectional Study of Heart Rate Variability among Swimmers, Runners, and Sedentary Adults

Abstract

Background: Heart rate variability (HRV) is a non-invasive marker of cardiac autonomic modulation and may differ according to habitual physical activity. Direct comparisons of young swimmers, runners, and sedentary adults remain limited. Objective: This study aimed to compare resting HRV and selected cardiovascular parameters among swimmers, runners, and sedentary adults aged 18–25 years and to explore sex-specific patterns. Methods: This hospital-based comparative cross-sectional study included 60 participants, comprising 20 swimmers, 20 runners, and 20 sedentary adults, with 10 males and 10 females in each group. Participants with cardiac, endocrine, or respiratory disease; substance dependence; chronic smoking or alcohol use; or medications likely to affect autonomic function were excluded. Resting heart rate, blood pressure, and 5-min lead II electrocardiogram recordings were obtained after a 15-min supine rest. Time-domain and frequency-domain HRV indices were analyzed. Results: Groups were similar in age and height. Sedentary participants had higher mean weight and body mass index than swimmers and runners. Resting heart rate did not differ significantly among groups. Systolic and diastolic blood pressure differed significantly across groups, with higher values in sedentary participants. Among HRV indices, low-frequency (LF) power differed significantly among the three groups (F = 3.983, P = 0.03), whereas standard deviation of normal-to-normal intervals (SDNN), root mean square of successive differences, pRR50, very-low-frequency, high-frequency (HF), and LF/HF ratio did not. Swimmers had lower SDNN and LF than sedentary participants. Sex-stratified analyses showed significant differences in LF among males and in SDNN, pRR50, and LF among females. Conclusion: Young adults engaged in regular swimming or running showed differences in selected resting cardiovascular and HRV measures compared with sedentary adults. Because the study was cross-sectional and based on a small sample, these findings indicate association rather than a causal effect of exercise.