Currently submitted to: JMIR mHealth and uHealth
Date Submitted: Apr 26, 2026
Open Peer Review Period: Apr 28, 2026 - Jun 23, 2026
(currently open for review)
Warning: This is an author submission that is not peer-reviewed or edited. Preprints - unless they show as "accepted" - should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.
Physical activity buffers physiological stress during high emotional distress: a wearable-derived prospective cohort study
ABSTRACT
Background:
Digital phenotyping using wearable devices and ecological momentary assessment (EMA) allows continuous monitoring of physiological and emotional states in real-world settings. However, identifying high-risk stress states remains challenging, particularly due to variability in individual physiological responses.
Objective:
This study aimed to evaluate the association between daily emotional distress and heart rate variability (HRV) and to assess whether physical activity buffers this relationship using longitudinal wearable and EMA data.
Methods:
The Smart Momentary Interactive Longitudinal Evaluation Study (SMILES) was a prospective cohort study conducted among STEM graduate students in the United States in 2025. Participants wore an Oura Ring Generation 3 continuously for five months and completed daily EMA surveys assessing emotional distress. The primary outcome was nightly HRV, measured as the root mean square of successive differences and log-transformed for analysis. Quantile regression within a quadratic inference function (QIF) framework was used to estimate associations at the 25th, 50th, and 75th percentiles of HRV, allowing assessment of how relationships differ across physiological stress states while accounting for within-participant correlation.
Results:
A total of 31 participants contributed 1,724 person-days of observation. Higher emotional distress was associated with lower HRV across the distribution, with the strongest effect observed at the lower HRV quantile ( = –0.094, 95% CI –0.111 to –0.078). A significant interaction between daily step count and emotional distress was observed across quantiles. Higher physical activity was associated with higher HRV on days of high emotional distress but showed little association on days of low-to-moderate distress.
Conclusions:
Combining wearable-derived physiological data with ecological momentary assessment can help identify high-risk stress states in real-world settings. Physical activity may buffer the association between emotional distress and HRV specifically during periods of elevated distress. These findings support the use of wearable-guided, just-in-time adaptive interventions to deliver personalized behavioral support when individuals are most vulnerable.
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