Effect of lowered muscle temperature on the physiological response to exercise in men

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Abstract
Summary The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12°C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5)°C to 30.5 (SD 1.7)°C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats · min−1 after 6 min of exercise, to 4 (SD 2) beats · min−1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.21 · min−1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia.