Core Temperature and Percentage of Dehydration in Professional Football Linemen and Backs During Preseason Practices

Context: Thermal responses of average-sized male subjects (mass of approximately 70 kg) may not accurately reflect the rate of heat storage in larger athletes with greater muscle mass. Objective: To determine if core temperature (Tc) is different in National Football League linemen and backs and if Tc is related to percentage of dehydration or sweat rate. Design: We measured Tc and sweat rate in professional football players during preseason twice-daily practices. Setting: Preseason training camp. Patients or Other Participants: Eight linemen (age = 26.6 ± 2.1 years, height = 191.8 ± 4.5 cm, mass = 134.8 ± 10.7 kg, body surface area = 2.61 ± 0.12 m2) and 6 backs (age = 27.0 ± 4.2 years, height = 185.0 ± 6.3 cm, mass = 95.6 ± 11.1 kg, body surface area = 2.19 ± 0.16 m2). Main Outcome Measure(s): We measured Tc using ingestible sensors. Resting Tc was recorded in the mornings of data collection with players dressed in shorts and then every 15 minutes during 2-hour practices in full pads or shells. Mass was recorded before and after practices for determining the percentage of dehydration. In 8 of the 14 subjects (4 linemen, 4 backs), sweat rate was calculated using the change in mass adjusted for fluid intake and urine production. Results: Height, mass, and body surface area were greater in linemen than in backs. We noted a linear trend over time for Tc in both groups. Maximal Tc was higher in linemen (38.65 ± 0.48°C) than in backs (38.44 ± 0.32°C), but linemen were less dehydrated than backs (−0.94 ± 0.6% versus – 1.3 ± 0.7%). Sweat rate was 2.11 ± 0.77 L/h and correlated significantly with body surface area (r = 0.77, P < .05). Maximal Tc was not correlated with either percentage of dehydration or sweat rate. Conclusions: Maximal Tc was not associated with percentage of dehydration or sweat rate. Linemen were less dehydrated but demonstrated higher Tc than backs during practice. Maximal Tc was generally achieved during live scrimmaging.