A Comparison Of Wearable Physiological Sensors That Estimate Core Temperature In Simulated Hot Work Conditions

Wearable physiological sensors (WPS) can provide real-time, continuous data to make immediate safety decisions based on how workers respond under a given heat exposure. Estimated core temperature (TEST) calculated from WPS can provide meaningful data on heat illness, strain, and risk, but they must be validated against gold standard measures and during intermittent physical activity in the heat. Two TEST algorithm models (2013 and 2020) are commonly used to assess heat strain in warfighters using heart rate in WPS; however, these models may have limitations when applied to non-military populations. PURPOSE: To examine the validity of TEST (2013 and 2020) compared to a validated measure [rectal temperature (TREC)] during physical activity in the heat in physically active men. METHODS: Twelve healthy men [age, 32 ± 7 years; peak oxygen consumption (VO2peak), 48.19 ± 7.09 ml·kg−1·min−1] completed four experimental trials (~4.5 hours) consisting of cycles of intermittent exercise. WPS were placed at three different locations [chest strap (CS), armband (AB), and wristwatch (WW)] and each incorporated TEST 2013 and 2020. Bland-Altman plots and linear regression were utilized to measure mean difference (MD), 95% limits of agreement (LoA), and coefficient of determination (R2), respectively. TREC was used as the reference measurement. An acceptable MD was determined as ≤0.27 °C. Data were also stratified by TREC value (<38.0 °C, 38.0-38.5 °C, 38.5-39.0 °C, 39.0-39.5 °C, >39.5 °C). RESULTS: The lowest and only acceptable MD was noted in CS, AB, and WW devices that utilized TEST 2020 (0.21 °C, 0.19 °C, 0.27 °C, respectively). For all WPS, 95% of the data fell between MD of -0.54 and 1.22 °C (95% LoA). R2 for all WPS ranged from 0.32-0.39. Poor agreement (>0.27 °C) occurred above 38.5 °C across all WPS TEST 2020 (CS:0.53-0.73 °C, AB: 0.52- 0.74 °C, WW:0.67-0.97 °C). CONCLUSION: Overall, WPS utilizing TEST 2020 demonstrated acceptable MD, but exhibited moderate variability, reflected by R2 values. As TREC increased above 38.5 °C, the MD for all WPS TEST 2020 was greater than the acceptable MD, thus indicating that WPS utilized in this study may not be acceptable for hyperthermic individuals performing intermittent work in the heat. Supported by: This study was funded by Vigilife.