Purpose: The study’s purpose was to investigate whether differences in local sweat rates on the upper body between American football linemen (L) and backs (B) exist independently of differences in metabolic heat production.
Methods: Twelve NCAA Division I American football players (6 linemen (mass = 141.6 ± 6.5 kg, body surface area (BSA) = 2.67 ± 0.08 m2) and 6 backs (mass = 88.1 ± 13.4 kg, BSA = 2.11 ± 0.19 m2)) cycled at a fixed metabolic heat production per unit BSA of 350 W·m−2 for 60 min in a climatic chamber (tdb [dry bulb temperature] = 32.4°C ± 1.0°C, twb [wet bulb temperature] = 26.3°C ± 0.6°C, v [air velocity] = 0.9 ± 0.1 m·s−1). Local sweat rates on the head, arm, shoulder, lower back, and chest were measured after 10, 30, and 50 min of exercise. Core temperature, mean skin temperature, and HR were measured throughout exercise.
Results: Because metabolic heat production per unit surface area was fixed between participants, the rate of evaporation required for heat balance was similar (L = 261 ± 35 W·m−2, B = 294 ± 30 W·m−2, P = 0.11). However, local sweat rates on the head, arm, shoulder, and chest were all significantly greater (P < 0.05) in linemen at all time points, and end-exercise core temperature was significantly greater (P = 0.033) in linemen (38.5°C ± 0.4°C) relative to backs (38.0°C ± 0.2°C) despite a ∼25% lower heat production per unit mass. The change in mean skin temperature from rest was greater in linemen (P < 0.001) after 15, 30, 45, and 60 min, and HR was greater in linemen for the last 30 min of exercise.
Conclusions: Football linemen sweat significantly more on the torso and head than football backs independently of any differences in metabolic heat production per unit BSA and therefore the evaporative requirements for heat balance. Despite greater sweating, linemen demonstrated significantly greater elevations in core temperature suggesting that sweating efficiency (i.e., the proportion of sweat that evaporates) was much lower in linemen.