Using mutual information [14,15], the time delay of each variable of the time series can be solved. Based on information theory, the mutual information between time series and its delay time series can be derived:
( ) = ( , ) = ( ) + ( ) − ( , ) .(3)
We compute the mutual information ( ) by the histogrambased statistic estimator [15], and , which makes ( ) to the first local minimum point, is regarded as the delay time of th variable. By calculating time series **data** of all subjects, reasonable reconstructing time lag can be obtained (the average time lag of 36 subjects is ankle = 17 ± 7.3, knee = 21 ± 5.8, and hip = 19 ± 8.3).