Climate change is increasing the number of hot days to which outdoor workers are exposed, thereby increasing their risk of heat illness. Currently, continuous monitoring of core temperature (Tc) is expensive, invasive, and impractical. The BioModule is a non-invasive physiological monitor that uses heart rate to provide an estimation of Tc, but its accuracy is unknown. PURPOSE: To test the association between measured gastrointestinal temperature (TGI) and estimated core temperature (Tc-est) from the BioModule device during outdoor work in a hot environment. METHODS: Twenty groundskeepers (18 men; mean±SD age = 38±8 y, body mass index = 31.5±7.5 kg/m2) swallowed an ingestible temperature sensor and strapped on a BioModule before work. TGI was collected every 15 minutes during the workday; Tc-est was determined by a 1-min average from the same time of day. Data collection occurred in Alabama during July and August (31.4±3.1 °C WBGT). Relationship between TGI and Tc-est was quantified using the repeated measures correlation coefficient (rrm). Agreement (bias±1.96 SD) between TGI and Tc-est was evaluated using the Bland-Altman method for repeated observations. RESULTS: There was a moderate, positive relationship between TGI and Tc-est (rrm = 0.56, p < 0.001). Agreement analysis indicated that Tc-est overestimated TGI (0.28±0.58 °C). The error between Tc-est and TGI was larger at lower temperatures, as indicated by a strong negative trend (Pearson’s r = −0.73). CONCLUSION: The BioModule provides an estimation of Tc that may be helpful as a guide during outdoor work in hot environments but should not be used for safety considerations or measurement of Tc . Funded by the Deep South Center for Occupational Safety and Health, a National Institute for Occupational Safety and Health Education and Research Center.
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