Assessing the Feasibility of Wearable Devices for Physiological Monitoring and Heat Risk Prediction in Outdoor Agricultural Workers.

BACKGROUND: Outdoor agricultural workers experience significant heat exposure, yet few studies have evaluated whether wearable sensors can reliably measure continuous physiological responses in real field conditions. This pilot study examined the feasibility and predictive utility of core temperature, hydration, heart rate, and movement data collected from commercially available wearables. METHODS: Thirty farmworkers in eastern North Carolina wore three devices, the CALERA core temperature sensor, the Nix Hydration Biosensor, and the Garmin Vivoactive smartwatch, during one July work shift. 1 min, physiological and environmental data were aligned to compute the modified Physiological Strain Index, mPSI. Device reliability, physiological responses, and heat exposure were summarized. Multi-linear regression and machine learning, Random Forest (RF) and Gradient Boosting Regression (GBR), models were evaluated to predict mPSI, using raw and smoothed predictors to estimate mPSI. RESULTS: CALERA retrieved 100 percent of the data, Garmin retrieved 97 percent, and Nix retrieved 80 percent. WBGT remained consistently high, approximately 28 to 29 degrees Celsius, and 12.6 percent of core temperature measurements exceeded 38 degrees Celsius. mPSI ranged from minimal to high heat strain, with 8.3 percent of observations at or above 5. Heart rate showed the strongest association with mPSI. The RF model using 60-min moving averages achieved the highest predictive accuracy with an R2 of 0.96 and a root mean squared error of 0.25. Wearables captured meaningful physiological patterns that corresponded with environmental heat exposure, and WBGT-based risk levels consistently overestimated heat strain relative to mPSI. CONCLUSION: Multi-sensor wearable systems are feasible for continuous heat strain monitoring and can support accurate prediction of heat-related risk among agricultural workers. This study is the first to evaluate the CALERA, Nix, and Garmin devices combined for heat strain monitoring in outdoor agricultural workers. By combining all three wearables in a field-based feasibility assessment, it addresses a key gap in validating consumer-grade technology for occupational safety in this high-risk workforce. The findings of the study support the use of wearable devices for real-time heat strain alerts, individualized hydration and work-rest guidance, and early warning systems to help prevent heat-related illness in physically demanding outdoor occupations.