Background: Heart rate variability (HRV), the beat-to-beat oscillation in the interval between successive cardiac cycles, has emerged as a non-invasive electrophysiological tool for evaluating autonomic nervous system (ANS) activity. The interplay between sympathetic and parasympathetic outflow to the sinoatrial node generates these oscillations, and altered HRV has been linked with adverse cardiovascular outcomes, metabolic disorders, and impaired stress adaptation. Aim: The present cross-sectional study was undertaken to characterize time-domain and frequency-domain HRV parameters in apparently healthy young Indian adults and to evaluate the influence of sex on autonomic balance. Materials and Methods: A total of 100 healthy adults (58 males, 42 females; aged 18–30 years) were recruited from the Department of Biochemistry, South India, between September 2008 and February 2009. After a 10-minute supine rest, a five-minute lead II electrocardiogram was acquired using a Powerlab 26T data acquisition system (ADInstruments, Australia). Time-domain (mean RR, SDNN, RMSSD, pNN50, triangular index) and frequency-domain (Total Power, LF, HF, LF n.u., HF n.u., LF/HF ratio) parameters were computed using LabChart Pro v8.1.21 HRV module. Independent samples t-test was used to compare male and female parameters; statistical significance was set at p<0.05. Results: Males demonstrated higher mean RR interval (814.6 ± 91.2 vs 772.4 ± 82.4 ms, p=0.018), SDNN (58.4 ± 14.6 vs 52.2 ± 13.2 ms, p=0.031), and LF/HF ratio (1.34 ± 0.42 vs 0.96 ± 0.34, p<0.001), suggesting a relative sympathetic predominance. Females exhibited higher HF (n.u.) values, indicating greater parasympathetic modulation. Conclusion: Healthy young Indian adults demonstrate clinically meaningful sex-based differences in autonomic balance, with male preponderance of sympathetic activity and female preponderance of parasympathetic tone. These population-specific HRV reference values are clinically relevant for the early detection of dysautonomia, cardiovascular risk stratification, and the design of targeted preventive strategies in young adults.

Heart rate variability; Autonomic nervous system; Sympathetic activity; Parasympathetic tone; LF/HF ratio; Healthy adults; Cardiovascular physiology.