Smartwatch-Derived Exercise Metrics as Predictors of Early Hypertension: A Prospective Observational Study

doi:10.21203/rs.3.rs-8238959/v1

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Smartwatch-Derived Exercise Metrics as Predictors of Early Hypertension: A Prospective Observational Study

https://doi.org/10.21203/rs.3.rs-8238959/v1

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Background:

Early detection of hypertension is crucial for cardiovascular prevention. Smartwatch-derived physiological and activity metrics may offer a practical tool for identifying individuals at risk before clinical onset.

Methods:

In this 12-month prospective study, 230 normotensive adults (30–60 years) were monitored using smartwatches recording heart rate variability, resting heart rate, and moderate-to-vigorous physical activity .

Results:

Twenty-eight participants (12.2%) developed hypertension. Those with new-onset hypertension had lower heart rate variability (42.6 ± 10.8 vs. 56.1 ± 12.9 ms, p < 0.001) and lower moderate-to-vigorous physical activity (38.4 ± 14.2 vs. 57.9 ± 16.7 min/day, p < 0.001). Reduced heart rate variability and moderate-to-vigorous physical activity independently predicted hypertension.

Conclusions:

Smartwatch-derived autonomic and exercise metrics can identify normotensive adults at risk of developing hypertension, supporting their role as digital biomarkers in preventive cardiology.

Hypertension

Heart rate variability

Physical activity

Smartwatch

Wearable technology

Hypertension is a leading modifiable risk factor for cardiovascular disease and premature mortality worldwide. Despite extensive public health efforts, nearly half of hypertensive individuals remain undiagnosed or untreated, highlighting the importance of early detection strategies. Conventional office-based blood pressure assessments often fail to capture dynamic physiological changes that precede the onset of sustained hypertension, particularly those related to autonomic dysfunction and physical inactivity.

Recent technological advances have enabled smartwatches to collect continuous cardiovascular and behavioral data under real-life conditions. Beyond heart rate tracking, these devices can measure heart rate variability (HRV), resting heart rate (RHR), and physical activity metrics such as moderate-to-vigorous physical activity (MVPA), VO₂max, and sedentary time, offering valuable insight into cardiovascular regulation. Reduced HRV has been associated with sympathetic overactivity and early vascular changes that predispose to hypertension, while low levels of MVPA contribute to endothelial dysfunction and elevated resting blood pressure[1–3].

Accumulating evidence suggests that HRV and daily activity levels may jointly reflect the autonomic–metabolic interplay underlying blood pressure regulation. Prospective studies have shown that lower HRV predicts incident hypertension in normotensive adults[4], and that regular aerobic activity reduces sympathetic tone and arterial stiffness, thus mitigating long-term hypertension risk[5, 6].

However, few studies have integrated multiple smartwatch-derived parameters into a single predictive framework, and most existing data rely on short-term or cross-sectional analyses.

Recent validation studies confirm the technical accuracy of smartwatch-based cardiovascular measurements[7–9], yet the clinical relevance of combining exercise and autonomic metrics to detect early hypertension remains largely unexplored. The integration of these digital biomarkers could provide a practical, noninvasive approach for identifying high-risk individuals before overt hypertension develops.

Therefore, the present prospective observational study aimed to assess whether smartwatch-derived exercise and autonomic parameters can predict incident hypertension during 12 months of follow-up in normotensive adults. We hypothesized that decreased HRV, reduced MVPA, and their interaction would independently predict early hypertension and that combining these smartwatch metrics with clinical variables would enhance predictive performance compared with conventional models.

Study design and population

This prospective observational study was conducted between January 2024 and January 2025 to evaluate whether smartwatch-derived exercise and autonomic parameters could predict incident hypertension among normotensive adults. A total of 230 participants aged 30–60 years were enrolled from outpatient cardiology and preventive medicine clinics. All participants provided written informed consent, and the study protocol was approved by the institutional ethics committee (Approval No: B.30.2.ATA.0.01.00/737) in accordance with the Declaration of Helsinki.

Inclusion criteria: age 30–60 years, baseline systolic BP < 140 mmHg and diastolic BP < 90 mmHg, continuous smartwatch use ≥ 20 days per month during follow-up, willingness to attend scheduled visits, and provision of written informed consent.

Exclusion criteria: known hypertension, coronary artery disease, heart failure or arrhythmia (including atrial fibrillation), current use of antihypertensive, antiarrhythmic, β-blocker, calcium-channel blocker, or ACE inhibitor therapy within 3 months before enrollment, diabetes mellitus, chronic kidney disease (eGFR < 60 mL/min/1.73 m²), thyroid dysfunction, autonomic neuropathy, BMI ≥ 35 kg/m², heavy smoking (> 20 cigarettes/day) or alcohol consumption (> 20 g/day), shift work or irregular sleep–wake patterns, sleep apnea syndrome, missing or incomplete smartwatch data (> 15% missing), technical incompatibility preventing data synchronization, pregnancy, lactation, hormonal therapy, or inability/unwillingness to attend the 12-month follow-up visit.

Smartwatch-derived parameters

Participants wore a validated smartwatch (Apple Watch Series 9 or equivalent) continuously for 12 months. The following parameters were automatically recorded and extracted through the device’s health API: resting heart rate (RHR, bpm), heart rate variability (HRV, RMSSD, ms), moderate-to-vigorous physical activity (MVPA, min/day), sedentary time (min/day), estimated VO₂max (ml/kg/min), sleep efficiency (% of time asleep/time in bed), and stress index (0–100). Monthly mean values and 30-day changes (ΔHRV, ΔRHR, ΔMVPA) were computed. Interaction indices (HRV×MVPA, RHR×Sedentary time) were derived to explore autonomic–activity relationships.

Clinical evaluation

Blood pressure (BP) was measured at baseline and at 12 months using a calibrated oscillometric device after 5 minutes of rest. The mean of the last two of three readings was recorded. Incident hypertension was defined according to the 2023 ESC/ESH guidelines as systolic BP ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg, or initiation of antihypertensive therapy during follow-up.

Statistical analysis

All analyses were performed using Python 3.12 (pandas, statsmodels, xgboost, lightgbm, shap). Continuous variables were expressed as mean ± SD and categorical variables as percentages. Normality was assessed using the Shapiro–Wilk test. Group comparisons were made with the Student’s t-test or Mann–Whitney U test for continuous variables, and the χ² or Fisher’s exact test for categorical data.

Multivariable logistic regression

Independent predictors of incident hypertension were identified using multivariable logistic regression including age, sex, BMI, HRV, RHR, MVPA, sedentary time, VO₂max, sleep efficiency, and interaction terms (HRV×MVPA, RHR×Sedentary). Adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Model calibration was assessed using the Hosmer–Lemeshow test, and discrimination using the area under the ROC curve (AUC).

Machine learning analysis

To complement traditional inference, predictive modeling was performed using Extreme Gradient Boosting (XGBoost) and Light Gradient Boosting Machine (LightGBM) with 10-fold stratified cross-validation. Feature importance was determined via SHAP (Shapley Additive Explanations) analysis. Performance metrics included ROC–AUC, F1-score, accuracy, and average precision, with cross-validated mean AUC and 95% CI reported.

Exploratory and interaction analyses

Restricted cubic spline regression was applied to assess non-linear associations. A partial dependence analysis illustrated the joint effect of HRV and MVPA, demonstrating the highest predicted risk among individuals with both low HRV (< 45 ms) and low MVPA (< 40 min/day). All tests were two-tailed, and a p < 0.05 was considered statistically significant.

Baseline characteristics

A total of 230 participants (mean age 45.8 ± 7.6 years, 52.6% women) completed the 12-month follow-up. During the study period, 28 individuals (12.2%) developed incident hypertension according to the ESC/ESH 2023 criteria. Participants who developed hypertension were older (48.7 ± 6.9 vs. 45.3 ± 7.4 years, p = 0.014), had a higher baseline BMI (28.2 ± 3.7 vs. 26.4 ± 3.1 kg/m², p = 0.009), and demonstrated lower mean HRV values (42.6 ± 10.8 vs. 56.1 ± 12.9 ms, p < 0.001) compared with normotensive subjects.

They also showed significantly lower daily MVPA (38.4 ± 14.2 vs. 57.9 ± 16.7 min/day, p < 0.001) and reduced VO₂max (34.7 ± 5.1 vs. 39.8 ± 5.8 mL/kg/min, p = 0.002).

Other parameters, including resting heart rate and sleep efficiency, showed non-significant trends toward higher risk in hypertensive converters. Table 1 summarizes baseline characteristics of participants according to hypertension status.

Table 1

*Baseline characteristics of participants according to incident hypertension status*
Variable	Total (n = 230)	No Hypertension (n = 202)	Incident Hypertension (n = 28)	p value
Age (years)	45.8 ± 7.6	45.3 ± 7.4	48.7 ± 6.9	0.014
Female sex, n (%)	121 (52.6)	108 (53.5)	13 (46.4)	0.49
Body mass index (kg/m²)	26.6 ± 3.3	26.4 ± 3.1	28.2 ± 3.7	0.009
Resting heart rate (bpm)	72.4 ± 7.9	72.1 ± 7.7	74.0 ± 8.8	0.22
Heart rate variability (HRV, RMSSD, ms)	54.3 ± 13.5	56.1 ± 12.9	42.6 ± 10.8	< 0.001
Moderate-to-vigorous physical activity (MVPA, min/day)	55.6 ± 17.9	57.9 ± 16.7	38.4 ± 14.2	< 0.001
Sedentary time (min/day)	540 ± 88	532 ± 84	598 ± 90	0.006
Estimated VO₂max (ml/kg/min)	39.2 ± 5.9	39.8 ± 5.8	34.7 ± 5.1	0.002
Sleep efficiency (%)	87.4 ± 4.8	87.6 ± 4.6	86.1 ± 5.5	0.19
Stress index (0–100)	45.1 ± 9.8	44.7 ± 9.6	48.0 ± 10.1	0.11
Smokers, n (%)	47 (20.4)	39 (19.3)	8 (28.6)	0.26
Follow-up duration (months)	12.0 ± 0.2	12.0 ± 0.2	12.0 ± 0.2	0.89

Multivariable logistic regression

In multivariable analysis, lower HRV (per 10-ms decrease, adjusted OR = 1.31, 95% CI 1.10–1.58, p = 0.003), lower MVPA (per 10-min decrease, OR = 1.18, 95% CI 1.04–1.36, p = 0.009), and higher BMI (per 1 kg/m² increase, OR = 1.12, 95% CI 1.01–1.26, p = 0.041) were independently associated with incident hypertension. The interaction term HRV × MVPA was statistically significant (p = 0.012), indicating a synergistic effect between autonomic balance and physical activity. The regression model showed good calibration (Hosmer–Lemeshow p = 0.64) and discrimination (AUC = 0.82, 95% CI 0.75–0.89).

Machine learning model performance

Using the same feature set, the XGBoost model achieved an average cross-validated ROC–AUC of 0.83 (95% CI 0.76–0.90), accuracy of 0.81, and F1-score of 0.74. The LightGBM model yielded comparable discrimination (AUC = 0.82, accuracy = 0.79). Both models demonstrated consistent calibration, with no evidence of overfitting across folds. The combined smartwatch + clinical model significantly outperformed the clinical-only baseline model (AUC = 0.83 vs. 0.68, p < 0.001 by DeLong test). Figure 1 displays ROC curves comparing the two models. Figure 2 presents the SHAP-based feature importance ranking, showing HRV RHR, and MVPA as the strongest contributors.

Exploratory and interaction analyses

Partial-dependence analysis revealed a clear non-linear relationship between HRV and MVPA (Fig. 3). Participants with both low HRV (< 45 ms) and low MVPA (< 40 min/day) exhibited the highest predicted risk (> 40%), whereas those maintaining high HRV (> 60 ms) and MVPA (> 60 min/day) had a risk below 10%. No significant sex-based or device-type interactions were observed.

Summary of key findings

Incident hypertension occurred in 12.2% of previously normotensive adults over 12 months.
Reduced HRV, lower MVPA, and higher BMI were independent predictors.
Smartwatch-derived parameters substantially improved discrimination compared to clinical data alone.
Machine-learning models confirmed the robustness of the physiological markers and their interaction effects.

In this prospective observational study, we found that smartwatch-derived exercise and autonomic parameters, particularly HRV and MVPA, were significant predictors of incident hypertension in normotensive adults during one year of follow-up. Individuals who developed hypertension demonstrated lower HRV, reduced physical activity, and increased sedentary time at baseline compared with those who remained normotensive. The integration of these wearable-derived indices with conventional clinical variables markedly improved predictive accuracy, highlighting the potential role of smartwatch-based metrics in early hypertension detection.

Our findings align with previous research suggesting that autonomic dysfunction and physical inactivity are among the earliest physiologic markers of blood pressure dysregulation. Reduced HRV, reflecting impaired parasympathetic modulation and sympathetic predominance, has been consistently associated with the development of hypertension. The Framingham Heart Study showed that diminished HRV independently predicted new-onset hypertension, even after adjusting for age and baseline blood pressure [4]. Similarly, Diaz and colleagues demonstrated that reduced HRV and elevated resting heart rate increased the risk of hypertension in a large African-American cohort [3]. These studies, along with our results, support the hypothesis that altered autonomic control precedes the clinical manifestation of sustained hypertension.

The inverse association between physical activity and hypertension risk observed in our cohort further reinforces the importance of lifestyle behaviors in cardiovascular regulation. Regular aerobic activity improves endothelial function, reduces arterial stiffness, and enhances baroreflex sensitivity, mechanisms that collectively lower blood pressure [10]. Participants with higher MVPA in our study exhibited better autonomic profiles and lower incident hypertension rates, suggesting a synergistic relationship between physical activity and autonomic function. The significant HRV×MVPA interaction term found in our regression model underscores this point, indicating that low HRV and low physical activity jointly identify a high-risk phenotype for hypertension development. These findings align with current guidelines emphasizing physical activity as a first-line preventive measure for blood pressure control [11, 12].

An important contribution of this study is the demonstration that real-world, continuously recorded smartwatch data can provide reliable physiological information relevant to cardiovascular risk. Prior research has validated the accuracy of smartwatch-derived HRV and heart rate metrics compared with gold-standard ECG and Holter recordings [13, 14]. While cuffless blood pressure estimation remains limited in precision, the use of surrogate physiologic markers such as HRV and MVPA circumvents calibration challenges and offers more stable longitudinal trends [15]. The present findings therefore highlight a pragmatic approach to hypertension risk assessment that relies on metrics already available in most commercially used wearable devices.

From a methodological standpoint, the consistency between logistic regression and machine learning results strengthens the robustness of our conclusions. Both XGBoost and LightGBM models identified HRV, resting heart rate, and MVPA as the most influential predictors of incident hypertension, with cross-validated AUC values exceeding 0.82. These models’ calibration performance suggests that complex, non-linear relationships within smartwatch-derived data can be effectively leveraged to identify individuals at increased risk. Importantly, these algorithms do not simply replicate conventional statistics but uncover subtle physiological interactions, supporting their future role in precision cardiovascular screening.

Clinically, these findings propose a paradigm shift from episodic blood pressure measurement to continuous physiological monitoring for early identification of at-risk individuals. Integrating wearable-derived autonomic and activity metrics into preventive cardiology could enable proactive lifestyle counseling and closer follow-up before the establishment of fixed hypertension. Such approaches could be particularly beneficial for younger adults, in whom hypertension is often unrecognized until later stages. Furthermore, the scalability and affordability of consumer smartwatches make this strategy feasible for population-level implementation.

Nonetheless, several limitations should be acknowledged. Despite careful device calibration, smartwatch-derived HRV and activity data are susceptible to environmental influences and algorithmic variability. The study cohort consisted of health-conscious volunteers, which may limit generalizability. Hypertension diagnosis relied on office-based measurements rather than continuous ambulatory monitoring, and biochemical correlates such as inflammatory or neurohormonal markers were not assessed. Additionally, while machine learning improved discrimination, the observational design precludes causal inference. Future studies should include larger, multi-ethnic populations, standardized device validation, and integration with vascular and metabolic biomarkers to enhance mechanistic understanding.

In conclusion, smartwatch-derived HRV and MVPA were independent predictors of early hypertension in normotensive adults, and their combination with clinical parameters substantially improved predictive accuracy. These findings underscore the potential of wearable devices as noninvasive, scalable tools for early detection and prevention of hypertension in real-life settings. As wearable technology becomes increasingly integrated into daily health monitoring, its application in cardiovascular risk stratification may transform hypertension prevention from reactive management to proactive digital surveillance.

Funding Declaration

Funding: No financial support was received for this study.

Clinical Trial Number

Clinical trial number: Not applicable.

Author Contribution

G.C.: Conceptualization, study design, data collection, data analysis, interpretation of results, manuscript drafting and critical revision.E.S. A.C.: Data collection, clinical evaluation, data interpretation, literature review, manuscript review and editing.All authors read and approved the final manuscript.

Data Availability

The data that support the findings of this study are available from Atatürk University Health Practice and Research Center (Atatürk Üniversitesi Sağlık Uygulama ve Araştırma Merkezi). However, restrictions apply to the availability of these data, which were accessed under institutional licence for the present study and are therefore not publicly available. The data may be obtained upon reasonable request and with permission from the Atatürk University Health Practice and Research Center.

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No competing interests reported.

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You are reading this latest preprint version

Smartwatch-Derived Exercise Metrics as Predictors of Early Hypertension: A Prospective Observational Study

Status:

Version 1

Abstract

Background:

Methods:

Results:

Conclusions:

Figures

Introduction

Methods

Results

Baseline characteristics

Multivariable logistic regression

Machine learning model performance

Exploratory and interaction analyses

Summary of key findings

Discussion

Declarations

Author Contribution

Data Availability

References

Additional Declarations

Status:

Version 1