JMIR Publications

ABSTRACT

Background:

Stress can have adverse effects on health and wellbeing. Informed by laboratory findings that Heart Rate Variability (HRV) decreases in response to an induced stress response, recent efforts to monitor perceived stress in the wild have focused on HRV measured through wearable devices. However, it is not clear that the well-established association between perceived stress and HRV replicates in naturalistic settings without explicit stress inductions and research-grade sensors.

Objective:

This work aims to quantify the strength of the associations between HRV and perceived daily stress using wearable devices in real-world settings.

Methods:

In the main study, 657 participants wore a fitness tracker and completed 14,695 Ecological Momentary Assessments (EMAs) assessing perceived stress, anxiety, positive affect, and negative affect across eight weeks. In the follow-up study, roughly a year later, 327 of the same participants wore the same fitness tracker and completed 1,373 EMAs assessing perceived stress at the most stressful time of the day over a one-week period. We used mixed-effects generalized linear models to predict EMA responses from HRV features calculated over varying time windows from 5-minutes long to 24h long.

Results:

Across all time windows, the models explained an average of 1% (Marginal R2) of the variance. Models using HRV features computed from an 8AM to 6PM time window (namely work hours) outperformed other time windows using HRV features calculated closer to the survey response time, but still explained a small amount (2.2% of the variance). HRV features that were associated with perceived stress were the LF to HF ratio (LF/HF), VLF power, Triangular Index, and SDANN. Additionally, we found that while HRV was also predictive of other related measures, namely anxiety, negative affect, and positive affect, it was a significant predictor of stress after controlling for these other constructs. In the follow-up study, calculating HRV when participants reported their most stressful time of the day was less predictive and provided a worse fit (R2 = 0.022) than the work hours time window (R2 = 0.032).

Conclusions:

A significant but small relationship between perceived stress and HRV was found. Thus, although HRV is associated with perceived stress in laboratory settings, the strength of that association diminishes in real-life settings. HRV might be more reflective of perceived stress in the presence of specific and isolated stressors and research-grade sensing. Relying on wearable-derived HRV alone might not be sufficient to detect stress in naturalistic settings and should not be considered a proxy for perceived stress but rather one component of a complex phenomenon.