Heat illness symptom index (HISI): A novel instrument for the assessment of heat illness in athletes

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 1 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 toot 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.