Kinetics of oxygen consumption during maximal exercise at different muscle temperatures

The aim of this study was to test at maximal exercise the hypothesis of the temperature-dependence of the kinetics of O-2 consumption (V-O2)) which predicts a greater O-2 deficit as muscle temperature is decreased. Six male subjects underwent 3 min exercise bouts at the minimum power eliciting maximum O-2 consumption (V-O2max), at normal temperature (A) and after cooling the thigh muscles by water immersion (C). Breath-by-breath VO2 was measured together with muscle blood flow (Qm), blood lactate accumulation (''early lactate'', eLa), heart rate and muscle temperature (Tm). The O-2 deficit was calculated by standard procedure. Net V-O2max was 2.92 +/- 0.85 (SD) and 3.19 +/- 0.71 l.min(-1) in C and A respectively (P < 0.05). Correspondingly, maximum power was 20 W lower in C than in A. At exercise start, Tm was 35.0 +/- 1.2 and 27.5 +/- 1.8 degrees C in A and C respectively. O-2 deficit was 2.25 +/- 0.53 and 3.05 +/- 1.12 l in A and C respectively. The corresponding eLa was 7.7 +/- 2.5 and 13.8 +/- 2.5 mM, (P < 0.05) while Qm was 376 +/- 92 and 290 +/- 50 ml.kg(-1) min(-1) (P < 0.05) in A and C, respectively. The eLa increase in C is associated with an impaired muscle blood flow and decreased muscle O-2 unloading, and does not completely explain the greater O-2 deficit in C. The unexplained fraction of the latter is perhaps accounted for by a greater net alactic O-2 deficit, in agreement with a temperature-dependent decrease of the velocity constants of oxidative reactions, as suggested by the tested hypothesis.