Effects of reduced muscle temperature on the oxygen uptake kinetics at the start of exercise

SHIOJIRI, T., SHIBASAKI, M., AOKI, K., KONDO, N. & KOGA, S. 1997. Effects of reduced muscle temperature on the oxygen uptake kinetics at the start of exercise. Acta Physiol Scand 159 , 327–333. Received 25 September 1995, accepted 5 November 1996. ISSN 0001–6772. Laboratory of Exercise and Sports Science, Yokohama City University; Division of Intelligence Science, Graduate School and Technology, Division of Education, Graduate School, Faculty of Human Development, Kobe University; and Applied Physiology Laboratory, Kobe Design University, Japan. The purpose of this study was to examine the effects of reduced muscle temperature (T_m ) on gas exchange kinetics and haemodynamics at the start of exercise. Six male subjects performed moderate cycle exercise under reduced (C) and normal (N) T_m conditions. T_m and rectal temperature were significantly reduced by immersion in cold water (by 6.6 °C and 1.8 °C, respectively). The increases in oxygen uptake (V˙o ₂) and oxygen pulse (V˙o ₂/HR) during phase 1 (abrupt increase after the start of exercise) were significantly lower under C than under N. The time constant for O₂ under C (36.0 ± 7.7 (SD) s) was significantly greater than under N (27.5 ± 4.4 s); however, the time constants of cardiac output under C (38.3 ± 16.6 s) and N (33.7 ± 18.5 s) were similar. These results suggest that the slower V˙o ₂ on-response under reduced T_m conditions is caused by decreased O₂ extraction in working muscle and/or by impairment of oxidative reactions by reduced muscle temperature.