Establishing a Physiological Strain Index Criterion During the Final Sixty Minutes of Heat Tolerance Testing: 2082 Board #238 May 30 2:00 PM - 3:30 PM
Medicine and Science in Sports and Exercise(2019)
Abstract
The heat tolerance test (HTT) assesses cardiorespiratory and thermoregulatory capacity during heat stress using heart rate (HR) and core temperature (Tcore) as pass/fail criteria, where HR and Tcore may not exceed 160 bpm and 38.6°C, respectively. Additional information regarding physiological stress and heat tolerance may be derived from the physiological strain index (PSI), which provides a singular physiological strain value using HR and Tcore measurements. To our knowledge, the change in PSI during the final 60 min of an HTT (ΔPSIF60) has not been evaluated as a potential criterion for classifying heat tolerance/intolerance during HTT. PURPOSE: The purpose of this study was to establish a criterion threshold for ΔPSIF60 and report on its ability to classify heat tolerance/intolerance during an HTT. METHODS: Seventy-seven US military men (age: 25 ± 5 yr, ht: 178.5 ± 7.1 cm, wt: 84.8 ± 10.1 kg) completed up to 120 min of continuous treadmill walking (3.3 mph, 4.0% grade) in 40°C and 40% relative humidity and were classified for their heat tolerance (n = 64) or heat intolerance (n = 13) using established Tcore and HR criteria. A ΔPSIF60 was calculated for, and compared between, heat tolerant (HT) and heat intolerant (HI) subjects using an independent sample t-test. A maximal normal accepted value for ΔPSIF60 was calculated by taking the mean value of ΔPSIF60 for HT subjects plus two standard deviations. RESULTS: ΔPSIF60 was significantly less in HT subjects than in HI subjects (0.54 ± 0.64 vs 1.95 ± 0.72; p < .001). For HT subjects, a ΔPSIF60 maximal normal accepted value was determined to be 1.82. CONCLUSION: Findings indicate that ΔPSIF60 appropriately differentiated HT from HI subjects during an HTT in this population of military personnel. Therefore, we report that exceeding a ΔPSIF60 of 1.82 may serve as an additional criterion for classifying heat intolerance during HTT. Further work on the validation of this maximal normal accepted value for ΔPSIF60 is needed.
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Key words
physiological strain index criterion,heat,testing,tolerance
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