Heat exchange during upper- and lower-body exercise

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Abstract
This study examined evaporative and dry heat exchange during upper- and lower-body exercise. Four male subjects performed arm-crank or cycle exercise at the same O2 uptake level (approximately 1.6 l/min) in an environment facilitating dry heat exchange [radiative and convective (R + C)] [ambient temperature (Ta) = 18 degrees C, dew-point temperature (Tdp) = 14 degrees C] and an environment facilitating evaporative heat loss (Esk) (Ta = 35 degrees C, Tdp = 14 degrees C). (R + C) was determined from the torso with a net radiometer and from the limbs with heat flow discs, whereas Esk was determined from the torso and limbs by ventilated dew-point sensors. In both environments neither esophageal temperature nor mean skin temperature were different between exercise types (P greater than 0.05). Torso (R + C) was significantly (P less than 0.05) greater during arm-crank than during cycle exercise in both environments. Torso Esk, as well as arm (R + C), and arm Esk were not different (P greater than 0.05) between exercise types in each environment. Leg (R + C) was greater (P less than 0.05) during cycle than during arm-crank exercise in the 18 degrees C environment, whereas leg Esk was greater (P less than 0.05) during cycle than during arm-crank exercise in the 35 degrees C environment. These data indicate that to compensate for greater torso sensible heat loss during upper body exercise lower body exercise elicits additional (R + C) or Esk from the legs. The avenue for this compensatory sensible and insensible heat loss depends upon the differential heat transfer coefficients which influence tissue conductivity and mass transfer.