Long-range correlations embedded in stride series were evaluated by means of balanced estimation of diffusion entropy.The results show that there is no statistically monotonical relation between the long-range correlation and the age.Especially,one cannot find long-range correlation characteristics in some samples.The comparison between the results of balanced estimation of diffusion entropy and detrended fluctuation analysis shows that some samples may obey Levy walk processes,instead of fractional Brownian motions.