ABSTRACT
CONTEXT: Exertional heat stroke is the third leading cause of death in US athletes. Elevations in core temperature in the digestive tract (TGI) 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. TGI variation in collegiate football linemen during intense "two-a-day" preseason practice. A secondary objective was to compare longitudinal TGI in offensive and defensive linemen. DESIGN: Cross-sectional observational study. SETTING: Division I Intercollegiate Athletics Football Program. INTERVENTIONS: TGI was monitored during consecutive preseason sessions. MAIN OUTCOME MEASUREMENTS: TGI, heat illness, weight changes, environmental stress, and subjective symptoms. RESULTS: Mean TGI were 37.8°C and 38.3°C during a.m. and p.m. practices, respectively. The a.m. practices revealed higher TGI gain (1.8°C) compared to p.m. (1.4°C). The p.m. practices had higher maximum TGI than a.m. practices (39.1°C versus 38.8, P=0.0001). Mean time to maximum temperature (Tmax) 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 TGI than defensive players (38.0°C vs. 36.7°C, P = 0.069). The rate of rise in TGI was significantly greater in a.m. practices. A decrease in rate of TGI rise was seen from the first to last a.m. practices of the week (P = 0.004). CONCLUSION: Significant TGI 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 TGI than defensive linemen. As players acclimatized, a decrease in the rate of TGI increase was appreciable, particularly in a.m. practices. Appreciating cumulative heat stress and variations in heat stress related to scheduling of practice is critical.
Subject(s)
Body Temperature/physiology , Football/physiology , Heat-Shock Response/physiology , Physical Exertion/physiology , Body Temperature Regulation/physiology , Cross-Sectional Studies , Gastrointestinal Tract/physiology , Heat Stroke/prevention & control , Hot Temperature/adverse effects , Humans , Male , Physical Fitness/physiology , Young AdultABSTRACT
BACKGROUND: Heatstroke is the third leading cause of death in athletics, and an important cause of morbidity and mortality in exercising athletes. There is no current method, however, for identifying milder forms of heat illness. In this pilot study, we sought to develop and provide initial validation for a Heat Illness Symptom Index scale (HISI) that would facilitate research in the assessment of milder forms of heat illness in athletes. METHODS: The study was designed as a multimodal prospective observational study of Division I football players during twice daily practices in southern Florida. We developed a 13-item scale that assessed symptoms that are suspected to occur during milder forms of heat illness. The resultant scale was assessed for reliability using Cronbach's alpha, and was assessed for construct validity by correlating scale scores with factors that are known to be related to heat illness. HISI scores, as well as data on perceived exertion, player position, and pre and post practice weights were collected from 95 athletes participating in late summer football practices. A total of 557 athlete sessions were analyzed. RESULTS: The mean score on the heat illness symptom scale was 12.1 (SD 13.8) and the median value was 8.0. Cronbach's alpha confirmed suitable internal consistency of the scale when assessed separately for each of the five morning practices (alpha = 0.91, 0.88, 0.82, 0.92, 0.85). There were statistically significant correlations of the scale score with weight loss during practice (P = 0.006), rating of perceived exertion (P = 0.005), player position (P < 0.0001), and ambient heat index (P = 0.02) as hypothesized. CONCLUSIONS: This pilot study provides initial validation for a novel symptom-based tool for use in assessing mild forms of heat illness in an athletic population. Further validation studies of the instrument, and correlating symptom scores with measures of core temperature, are needed and planned.
