Validity of the peak velocity to detect physical training improvements in athymic mice

This study comprises two complementary experiments with athymic Balb/c (Nu/Nu) mice. In experiment 1, the aim was to verify the reproducibility of the peak velocity (V_Peak) determined from the incremental test. The second experiment aimed to assess the V_Peak sensitivity to prescribe and detect modulations of the physical training in athymic nude mice. Sixteen mice were submitted to two incremental treadmill tests separated by 48-h (Experiment 1). The test consisted of an initial warm-up of 5 minutes. Subsequently, animals initiated the tests at 8 m min^-1 with increments of 2 m min^-1 every 3 minutes. The V_Peak was determined as the highest velocity attained during the protocol. In experiment 2, these animals were randomly allocated to an exercise group (EG) or a control group (CG). The training protocol consisted of 30-min of treadmill running at 70% of the V_Peak five times a week for 4 weeks. High indexes of reproducibility were obtained for V_Peak (Test = 19.7 ± 3.6 m min^-1; Retest = 19.2 ± 3.4 m min^-1; p = 0.171; effect size = 0.142; r = 0.90). Animals from the EG had a significant increase of V_Peak (Before = 18.4 ± 2.7 m min^-1; After = 24.2 ± 6.0 m min^-1; p = 0.023). Conversely, a significant decrease was observed for the CG (Before = 21.1 ± 3.9 m min^-1; After = 15.9 ± 2.7 m min^-1; p = 0.038). The V_Peak is a valid parameter for exercise prescription in studies involving athymic nude mice.