Validation of a Ramp Running Protocol for Determination of the True VO(2max) in Mice

In the field of comparative physiology, it remains to be established whether the concept of VO(2max) is valid in the mouse and, if so, how this value can be accurately determined. In humans, VO(2max) is generally considered to correspond to the plateau observed when VO(2) no longer rises with an increase in workload. In contrast, the concept of VO(2peak) tends to be used in murine studies. The objectives of the present study were to determine whether (i) a continuous ramp protocol yielded a higher VO(2peak) than a stepwise, incremental protocol, and (ii) the VO(2peak) measured in the ramp protocol corresponded to VO(2max). The three protocols (based on intensity-controlled treadmill running until exhaustion with eight female FVB/N mice) were performed in random order: (a) an incremental protocol that begins at 10 m.min(−1) speed and increases by 3 m.min(−1) every 3 min. (b) a ramp protocol with slow acceleration (3 m.min(−2)), and (c) a ramp protocol with fast acceleration (12 m.min(−2)). Each protocol was performed with two slopes (0 and 25°). Hence, each mouse performed six exercise tests. We found that the value of VO(2peak) was protocol-dependent (p < 0.05) and was highest (59.0 ml.kg (0.75).min(−1)) for the 3 m.min(−2) 0° ramp protocol. In the latter, the presence of a VO(2max) plateau was associated with the fulfillment of two secondary criteria (a blood lactate concentration >8 mmol.l(−1) and a respiratory exchange ratio >1). The total duration of the 3 m.min(−2) 0° ramp protocol was shorter than that of the incremental protocol. Taken as a whole, our results suggest that VO(2max) in the mouse is best determined by applying a ramp exercise protocol with slow acceleration and no treadmill slope.