Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise

A study was undertaken in man to investigate whether during moderate cold stress, the proportion of carbohydrate (CHO) oxidized is increased, and whether prior prolonged exhaustive exercise compromises thermoregulation. Eight euglycaemic men were cooled by a liquid-conditioned suit (1) after an overnight fast (Con) and (2) approximately 2 h after an exercise protocol in which CHO availability was substantially lowered (Post-Ex). The cooling stimulus lasted 90 min (Cooling) and was preceded by a 30 min thermo-neutral baseline phase (Base). In Con, aural temperature (T(aural)) and the rate of CHO oxidized (CHOox) were not altered from the values at Base during Cooling, whereas the following were increased: the rate of heat production (Hprod, approximately 1.9-fold), thigh electromyographical activity (EMG, approximately 2.5-fold), and the rate of fat oxidized (FATox, approximately 1.7-fold). In Post-Ex, T(aural) did not decrease from the value at Base during Cooling, and compared with Con, EMG, CHOox and the rate of heat loss were not different, whereas Hprod (P < or = 0.01), FATox (P < or = 0.01) and mean skin temperature (P < or = 0.01) were higher, and T(aural) was lower (P < or = 0.05). It is concluded that during moderate cold stress, shivering thermogenesis is supported by an increase in the oxidation of fat, and despite an alteration in the initial thermoregulatory responses to Cooling approximately 2 h after exhaustive exercise, thermoregulation was not impaired.