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 (T(c)) is different in National Football League linemen and backs and if T(c) is related to percentage of dehydration or sweat rate. DESIGN We measured T(c) 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 T(c) using ingestible sensors. Resting T(c) 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 T(c) in both groups. Maximal T(c) was higher in linemen (38.65 +/- 0.48 degrees C) than in backs (38.44 +/- 0.32 degrees 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 T(c) was not correlated with either percentage of dehydration or sweat rate. CONCLUSIONS Maximal T(c) was not associated with percentage of dehydration or sweat rate. Linemen were less dehydrated but demonstrated higher T(c) than backs during practice. Maximal T(c) was generally achieved during live scrimmaging.