Gastrointestinal Temperature Trends in Football Linemen During Physical Exertion Under Heat Stress

Context: Exertional heat stroke is the third leading cause of death in US athletes. Elevations in core temperature in the digestive tract (T(GI)) have correlated with core temperature and are possible indicators of those at increased risk of heat stroke. Objective: The primary objective was to compare a.m. vs. p.m. T(GI) variation in collegiate football linemen during intense two-a-day preseason practice. A secondary objective was to compare longitudinal T(GI) in offensive and defensive linemen. Design: Cross-sectional observational study. Setting: Division I Intercollegiate Athletics Football Program. Interventions: T(GI) was monitored during consecutive preseason sessions. Main Outcome Measurements: T(GI), heat illness, weight changes, environmental stress, and subjective symptoms. Results: Mean T(GI) were 37.8 degrees C and 38.3 degrees C during a.m. and p.m. practices, respectively. The a.m. practices revealed higher T(GI) gain (1.8 degrees C) compared to p.m. (1.4 degrees C). The p.m. practices had higher maximum T(GI) than a.m. practices (39.1 degrees C versus 38.8, P = 0.0001). Mean time to maximum temperature (T(max)) was 1 hr and 30 min for a.m. and 1 hr and 22 min for p.m. practices. Offensive linemen trended toward higher mean T(GI) than defensive players (38.0 degrees C vs. 36.7 degrees C, P = 0.069). The rate of rise in T(GI) was significantly greater in a.m. practices. A decrease in rate of T(GI) rise was seen from the first to last a.m. practices of the week (P = 0.004). Conclusion: Significant T(GI) elevations in asymptomatic athletes are common in extreme heat during football practice. Intense a.m. practices in full gear result in higher net temperature gain and rate of temperature gain than p.m. practices. Offensive linemen trended toward higher T(GI) than defensive linemen. As players acclimatized, a decrease in the rate of T(GI) increase was appreciable, particularly in a.m. practices. Appreciating cumulative heat stress and variations in heal stress related to scheduling of practice is critical.