Core Temperature Response During Two-a-Day Practices in NCAA Division-1 College Football

Abstract

0368 PURPOSE: To determine changes in core temperature during the first day of twoa-day football practices. In preliminary work, we showed that core temperature in college football players increased rapidly and remained high during a sustained (90 min) intense strength and conditioning pre-season workout. In this study, we tested eight players on their first day of two-a-day practice. METHODS: Sweat loss, fluid intake, and core temperature (Tc) were measured during morning and evening practices each lasting ∼2.2 h. Change in bodyweight, corrected for fluid intake and urine loss, was used to estimate gross sweat loss (GSL). Voluntary fluid intake (water and sports drinks) was measured by recording pre-and post-practice bottle weights. Without interfering with normal drills, Tc was measured ∼10 min intervals using ingestible temperature sensors (HTI Technologies). RESULTS: The average level of heat stress during practices was 24 ± 1.8° C WBGT. Total fluid consumed was 2.9 ± 1.1 L per session, and sweat rate was determined to be 1.8 ± 0.5 L per hour. Average GSL was 4.1 ± 1.1 L and resulted in a net 1.2 ± 1 kg weight loss (0.9 ± 0.7% dehydration). Mean Tc was 37.4 ± 0.3° C at baseline and increased to 38.5 ± 0.4° C by the end of practice. Change in Tc was 1.1 ± 0.4° C (range 0.4 – 1.9° C). CONCLUSIONS: Moderate environmental conditions, minimal dehydration, and varying intensity during two-aday practices resulted in an increased, but not excessive, stable core temperature. These data suggest the varying intensity of two-a-day practices (held during lower heat stress periods of the day) in combination with rest breaks, provides enough recovery time to prevent extreme increases in core temperature.