Effects of a Power Nap on the Very Low Frequency Component of Heart Rate Variability

Objective:This exploratory study investigates the relationship between heart rate (HR) and the very low frequency (VLF) component of heart rate variability (HRV) during a power nap. While HR is commonly used as a linear indicator of physiological state, we hypothesize that VLF captures non-linear autonomic dynamics that are not reflected in heart rate alone. Methods: Physiological data were collected from six healthy adults (3 males, 3 females) using wearable ECG sensors. Three 5-minute segments were analyzed for each participant: pre-sleep, sleep/nap, and post-awakening. Frequency-domain HRV indices were calculated, and statistical analyses included Pearson’s correlation coefficient and Cohen’s d to evaluate linear relationships and effect sizes. Results: A negligible correlation was observed between HR and VLF (r = − 0.12, R² = 0.014), indicating that heart rate explains only 1.4% of the variance in VLF power. During the post-awakening phase, VLF power showed a pronounced surge (exceeding 10,000 ms² in some cases), despite relatively stable HR, suggesting a rapid autonomic “reboot.” Gender comparisons revealed small effect sizes for mean HR (d = 0.21) and VLF (d = 0.08); however, males exhibited substantially greater HR variability than females, indicating differences in autonomic stability rather than mean activity. Conclusion: These findings demonstrate a clear decoupling between linear heart rate and non-linear autonomic oscillations during a power nap cycle. VLF appears to act as an early indicator of physiological recovery and arousal, whereas HR reflects a delayed or saturated response. Frequency-domain HRV analysis, particularly VLF, is therefore essential for assessing recovery quality in short-term nap interventions, where linear metrics alone fail to capture underlying autonomic complexity.