Monitoring heat strain: the effect of sensor type and location on single-site and mean skin temperature during work in the heat

Purpose Elevations in skin temperature and heat strain reduce tolerance to work in the heat. This study assessed agreement between mean (eight sites) and single-site skin temperature, measured by a conductive or infrared sensor, during exercise in the heat. Methods Twelve males (age: 24.2 +/- 3.7 years; height: 180 +/- 6.5 cm; body mass: 82.9 +/- 9.5 kg; body fat: 16.0 +/- 6.5%) volunteered to participate in two trials. Thirty minutes of seated rest was followed by 60 min of treadmill walking (4.5 km.h-1, 1%) inside an environmental chamber (35.5 +/- 0.2 degrees C dry bulb, 50.7 +/- 2.5% relative humidity) wearing either an athletic (ATH: t-shirt, shorts, shoes) or a chemical protective ensemble (CPE: ATH plus coverall and respirator). Skin temperature was measured on the axilla with a conductive sensor -(Tsk-C) and an infrared sensor -(Tsk-I) and compared to mean skin temperature ((T) over bar (sk), 8-site conductive sensors). Rectal temperature and heart rate were measured and used to calculate the adaptive physiological strain index (aPSI). Results Skin temperature on the chest, scapula, and thigh showed acceptable agreement with (T) over bar (sk) (mean difference < 0.5 degrees C and limits of agreement +/- 1.0 degrees C) in both ATH and CPE. Skin temperature on the axilla overestimated <(T)over bar>(sk) in ATH -(Tsk-C: 1.5 +/- 0.8 degrees C; -Tsk-I: 2.2 +/- 1.2 degrees C) and CPE -(Tsk-C: 1.1 +/- 0.9 degrees C; -Tsk-I: 1.8 +/- 1.1 degrees C). Significant differences (p < 0.001) were observed in aPSI using -Tsk-I (ATH: 5.7 +/- 1.0, CPE: 8.3 +/- 1.1) and -Tsk-C (ATH: 5.4 +/- 1.0, CPE 7.8 +/- 1.0) compared to <(T)over bar>(sk) (ATH: 5.2 +/- 1.0, CPE: 7.4 +/- 1.0). Conclusion The overestimate of mean skin temperature had a significant influence on the aPSI, which has important implications for real-time monitoring and risk management of personnel working in hot environments.

Automated summary

Skin temperature in different body parts showed good agreement with mean skin temperature during exercise, except for the axilla which overestimated the mean skin temperature. This overestimation had a significant impact on the adaptive physiological strain index, highlighting the importance of accurate monitoring in hot environments for personnel safety.