To examine whether the day-to-day coupling between diary-based sleep metrics and daytime RMSSD varies according to baseline insomnia symptom burden.
Approach:
Study Design: Secondary analysis of a publicly available dataset pairing daily sleep diaries with wearable-derived HRV summaries collected over four weeks.
Participants: 49 healthy adults aged 21–43 years were monitored, providing at least one day of both sleep diary data and eligible daytime HRV windows.
Data Collection: Participants completed daily sleep diaries and wore a smartwatch for HRV monitoring during waking hours.
Key Findings:
Stronger within-person coupling between sleep-continuity metrics and daytime RMSSD was observed among participants with higher baseline insomnia symptom burden.
Sleep latency was treated as a sleep-initiation metric, while sleep efficiency and WASO were used for sleep continuity.
Interpretation:
The study clarifies how insomnia symptoms may influence the relationship between self-reported sleep metrics and cardiac vagal physiology.
Limitations:
The study is exploratory and based on a fixed, publicly available dataset without new data collection.
Sample size was limited to 49 participants, which may affect the generalizability of findings.
Conclusion:
The findings suggest that insomnia severity may modulate the relationship between sleep patterns and heart rate variability.
