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The physiological strain index modified for trained heat-acclimatized individuals in outdoor heat

International Journal of Sports Physiology and Performance, ISSN: 1555-0273, Vol: 14, Issue: 6, Page: 805-813
2019
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Article Description

Purpose: To determine if the Physiological Strain Index (PSI), in original or modified form, can evaluate heat strain on a 0–10 scale, in trained and heat-acclimatized men undertaking a competitive half-marathon run in outdoor heat. Methods: Core (intestinal) temperature (TC) and heart rate (HR) were recorded continuously in 24 men (mean [SD] age = 26 [3] y, VOpeak = 59 [5] mL·kg·min). A total of 4 versions of the PSI were computed: original PSI with upper constraints of TC 39.5°C and HR 180 beats·min (PSI) and 3 modified versions of PSI with each having an age-predicted maximal HR constraint and graded TC constraints of 40.0°C (PSI), 40.5°C (PSI), and 41.0°C (PSI). Results: In a warm (26.1–27.3°C) and humid (79–82%) environment, all runners finished the race asymptomatic in 107 (10) (91–137) min. Peak TC and HR were 39.7°C (0.5°C) (38.5–40.7°C) and 186 (6) (175–196) beats·min, respectively. In total, 63% exceeded TC 39.5°C, 71% exceeded HR 180 beats·min, and 50% exceeded both of the original PSI upper TC and HR constraints. The computed heat strain was significantly greater with PSI than all other methods (P < .003). PSI >10 was observed in 63% of runners with PSI, 25% for PSI, 8% for PSI, and 0% for PSI. Conclusions: The PSI was able to quantify heat strain on a 0–10 scale in trained and heat-acclimatized men undertaking a half-marathon race in outdoor heat, but only when the upper TC and HR constraints were modified to 41.0°C and age-predicted maximal HR, respectively.

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