Estimation of anaerobic energy production and efficiency in rats during exercise.

To assess the effects of gradient and running speed on efficiency of exercise, and to evaluate contributions of oxidative and anaerobic energy production (Ean) during locomotion, two sets of experiments were performed. The caloric expenditures of rats were determined from O2 consumption (VO2) while they ran at three speeds (13.4, 26.8, and 43.1 m/min) on five grades (1, 5, 10, 15, and 20%). In addition, lactate turnover (LaT) and oxidation (Laox) were determined on rats at rest or during running at 13.4 and 26.8 m/min on 1% grade, respectively. Lactate production not represented in the VO2 (i.e., Ean) was calculated from the LaT not accounted for by oxidation [(LaT an) = LaT-Laox)]. The Ean was calculated as: Ean = [LaT an(mumol/min)] [1.38 ATP/La] [11 mcal/mumol ATP]. Gross efficiency of exercise (the caloric equivalent of external work/caloric equivalent of VO2 X 100) ranged from 1.7 to 4.5%. Apparent efficiency (the inverse of the regression of caloric equivalent of VO2 on the caloric equivalent of work X 100) ranged from 20.5 to 26.4% and reflected the metabolic response of rats to applied external work. The contribution of Ean to total energy turnover ranged from 1.6% at rest to 0.8% during running at 13.4 m/min on a 1% grade. Despite active LaT during steady-state exercise, Ean contributes insignificantly to total energy transduction, because over 70% of the lactate produced is removed through oxidation. VO2 adequately represents metabolism under these conditions.