Temperature-induced changes in metabolic and hormonal responses to intensive dynamic exercise.

Seven male subjects performed intensive cycle exercise to exhaustion at subnormal muscle temperature (Tm, 29 +/- 2.8 degrees C). Exercise at exactly the same rate of exercise and duration (370 +/- 34 W, 1.5 +/- 0.15 min) was then repeated with normal Tm (35 +/- 0.9 degrees C). During exercise both the arterial (a) and femoral venous (fv) contents of oxygen were significantly higher at subnormal than at normal Tm, because of the higher haemoglobin concentration, but the a-fv oxygen difference was the same in the two situations. The rate of increase in lactate concentration in both arterial and venous blood during exercise was the same in two situations. During exercise the plasma concentrations of adrenaline and noradrenaline in arterial and venous blood were significantly higher at subnormal than at normal Tm. At rest and after exercise the calf blood flow was significantly reduced at subnormal Tm. At the end of exercise the concentrations of glucose-6-phosphate and lactate in the muscle were significantly higher at subnormal Tm than in the muscle of normal temperature. These findings suggest that there was a greater increase in glycolysis in the muscle of subnormal temperature during exercise, possibly as a result of impaired work efficiency and/or reduced blood flow in the cold muscle.