The Heat Strain of Various Athletic Surfaces: A Comparison Between Observed and Modeled Wet-Bulb Globe Temperatures

Context: The National Athletic Trainers' Association recommends using onsite wet-bulb globe temperature (WBGT) measurement to determine whether to modify or cancel physical activity. However, not all practitioners do so and instead they may rely on the National Weather Service (NWS) to monitor weather conditions. Objective: To compare regional NWS WBGT estimates with local athletic-surface readings and compare WBGT measurements among various local athletic surfaces. Design: Observational study. Setting: Athletic fields. Main Outcome Measure(s): Measurements from 2 identical WBGT devices were averaged on 10 athletic surfaces within an NWS station reporting radius. Athletic surfaces consisted of red and black all-weather tracks (track), blue and black hard tennis courts (tennis), nylon-knit artificial green turf, green synthetic turfgrass, volleyball sand, softball clay, natural grass (grass), and a natural lake (water). Measurements (n = 143 data pairs) were taken over 18 days (May through September) between 1 PM and 4: 30 PM in direct sunlight 1.2 m above ground. The starting location was counterbalanced across surfaces. The NWS weather data were entered into an algorithm to model NWS WBGT. Results: Black tennis, black track, red track, and volleyball sand WBGT recordings were greater than NWS estimates (P <= .05). When all athletic-surface measurements were combined, NWS (26.85 degrees C +/- 2.93 degrees C) underestimated athletic-surface WBGT measurements (27.52 degrees C +/- 3.13 degrees C; P < .001). The range of difference scores (-4.42 degrees C to 6.14 degrees C) and the absolute mean difference (1.71 degrees C +/- 1.32 degrees C) were large. The difference between the onsite and NWS WBGT measurements resulted in misclassification of the heat-safety activity category 45% (65/143) of the time (chi(2)(1) = 3.857, P = .05). The WBGT of water was 1.4 degrees C to 2.7 degrees C lower than that of all other athletic surfaces (P = .04). We observed no other differences among athletic surfaces but noted large WBGT measurement variability among athletic playing surfaces. Conclusions: Clinicians should use an onsite WBGT device to determine environmental conditions and the need for modification of athletic events, especially as environmental conditions worsen. Given the large WBGT variability among athletic surfaces, WBGT measurements should be obtained from each athletic surface.