Effect of exercise on the gait pattern in the chronic MPD. The representative pattern of step length time series from a probenecid control mouse, a sedentary chronic MPD mouse, and an exercised chronic MPD mouse 12 weeks after MPTP/probenecid treatment were shown at top. The calculated gait pattern certainties in terms of approximate entropy (ApEn) for the three groups of animals were respectively shown in the bar graph below. A larger ApEn value denotes a more variable movement pattern, which was significantly demonstrated by the sedentary chronic MPD when compared with the control group of animals (*P = 0.0001). The ApEn value for the exercised chronic MPD was significantly lower suggesting a more consistent gait pattern than that of the sedentary chronic MPD (**P = 0.007). The gait pattern consistency (ApEn value) in the control group and exercised chronic MPD group were not statistically different.