| Summary: | There are many occupational and professional careers that demand performance at the highest levels of function possible in hot environments. During heat exposure, the body undergoes a battery of physiological changes in response high heat stress. A problem arises when current physiological strain models are applied towards instantaneous monitoring of physiological strain in field settings. The Montana Center for Work Physiology and Exercise Metabolism has developed a novel equation to assess physiological strain, coined the Physiological Strain Scale (PSS), using the metrics of skin temperature (chest) and heart rate. This purpose of this study was to validate the new equations through previously collected data from 2 field studies (N=29, N=12), which varied in workload (Firefighting duties vs. Controlled Wattage Ride) , intensity, and environmental conditions (WLFF: 27.4 °C ± 3.61 °C and 6.5 mph ± 3.0 mph vs. Cycling: 12.5°C ± 7.1°C and 6.2 mph ± 5.7 mph). Core temperature, skin temperature (chest), and heart rate were continuously monitored in both studies. Accuracy was assessed between the gold standard PSI and the novel PSS equation by a 2 x 5 ANOVA between the number of overall minutes spent in the following groupings: No/Little= <2, Low=2.1-4, Moderate= 4.1-6, High= 6.1-8, Very high= >8. The novel equation of PSS demonstrated accuracy and reliability in the higher ambient temperature, lower wind speed environment when compared to PSI. However, PSS measured physiological strain to be significantly less in the lower temperature, higher wind speed environment when compared to PSI. This data suggests PSS is reliable in environments with a low Tcore-Tskin gradient, but may need adjustment in environments with a large Tcore-Tskin gradient.
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