Fat (max) as an index of aerobic exercise performance in mice during uphill running

Endurance exercise performance has been used as a representative index in experimental animal models in the field of health sciences, exercise physiology, comparative physiology, food function or nutritional physiology. The objective of the present study was to evaluate the effectiveness of Fat(max) (the exercise intensity that elicits maximal fat oxidation) as an additional index of endurance exercise performance that can be measured during running at submaximal exercise intensity in mice. We measured both Fat(max) and Vo(2 peak) of trained ICR mice that voluntary exercised for 8 weeks and compared them with a sedentary group of mice at multiple inclinations of 20, 30, 40, and 50° on a treadmill. The Vo(2) at Fat(max) of the training group was significantly higher than that of the sedentary group at inclinations of 30 and 40° (P < 0.001). The running speed at Fat(max) of the training group was significantly higher than that of the sedentary group at inclinations of 20, 30, and 40° (P < 0.05). Blood lactate levels sharply increased in the sedentary group (7.33 ± 2.58 mM) compared to the training group (3.13 ± 1.00 mM, P < 0.01) when running speeds exceeded the Fat(max) of sedentary mice. Vo(2) at Fat(max) significantly correlated to Vo(2 peak), running time to fatigue, and lactic acid level during running (P < 0.05) although the reproducibility of Vo(2 peak) was higher than that of Vo(2) at Fat(max). In conclusion, Fat(max) can be used as a functional assessment of the endurance exercise performance of mice during submaximal exercise intensity.