The Lyapunov exponent spectrum of the COP signal has been applied to characterize the human standing activity as chaotic and as an aid to identify arrhythmias. The minimal distance to define these two points of the phase space is , the range of which has been given in Section 3.4. In order to obtain a uniform evaluation and to avoid the interference of the evaluation of different parameters, was set at 1000, which was within a reasonable range. Different working parameters of may lead to different conclusions about the same **data** [25]. If we change the value, the metric would be inaccurate or even fail to assess human standing ability. A sensitivity analysis of parameter will be carried out by using the Lyapunov exponent spectrum in our future work. 