Using Wet Bulb Globe Temperature and Physiological Equivalent Temperature as Predicative Models of Medical Stress in a Marathon: Analysis of 30 Years of Data From the Twin Cities Marathon.

Objectives: : Assess the relationships between wet bulb globe temperature (WBGT) and physiologic equivalent temperature (PET) at the start of a northern latitude marathon and their associations with medical stress and transfers to the emergency room (ER) when the race environment is unexpectedly warm, and participants are not acclimatized.

Design: : Retrospective review.

Setting: : Twin Cities Marathon from 1990 to 2019.

Participants: : Runners competing in the Twin Cities Marathon.

Independent Variables: : Start WBGT (prospectively collected) and PET (retrospectively calculated).

Main Outcome Measures: : Marathon race starters and finishers and race day medical data (eg, medical stress, number of medical encounters, and number of ER visits).

Results: : The mean WBGT was 7.4°C (range -1.7°C to 22.2°C), and the meant PET was 5.2°C (range -16.7°C to 25.9°C). PET was not determined to be a significant predictor of medical stress (P = 0.71); however, a significant quadratic association between WBGT and medical stress was found (P = 0.006). WBGT (P = 0.002), but not PET (P = 0.07), was a significant predictor of the number of ER visits.

Conclusions: Start WBGT was a better predictor of medical stress and ER visits than PET at the Twin Cities Marathon over a 30-year period. The start WBGT may be a better tool to predict race day environment medical safety.