Twenty-four adult male CF1 mice were assigned to three groups: non-runners control, level running exercise (0 degrees incline) and downhill running exercise (16 degrees decline). Exercise groups were given running treadmill training for 5 days/week over 8 weeks. Blood lactate analysis was performed in the first and last exercise session. Mice were sacrificed 48 h after the last exercise session and their solei (citrate synthase activity) and brain cortices (BDNF levels and cytochrome c oxidase activity) were surgically removed and immediately stored at -80 degrees C for later analyses. Training significantly increased (P<0.05) citrate synthase activity when compared to untrained control. Blood lactate levels classified the exercise intensity as moderate to high. The downhill exercise training significantly reduced (P<0.05) brain cortex cytochrome c oxidase activity when compared to untrained control and level running exercise groups. BDNF levels significantly decreased (P<0.05) in both exercise groups.