ABSTRACT
Objective To solve the problem in motion signal extraction due to nonstationarity.Methods The calf angular acceleration signal was taken as an example,and the time-frequency analysis was carried out by using Hilbert-Huang transform (HHT).Then,the empirical mode decomposition (EMD) of the signal was executed to obtain some intrinsic mode functions (IMFs),and then all or some intrinsic mode functions were subjected to a Hilbert transform to obtain Hilbert spectrum of the signal.Results In the mode of stomping,walking and falling,when the test-feet touched the ground,the energy was concentrated at the frequencies of 4 Hz,3 Hz and 2 Hz,and the time-frequency resolution was higher,and the information of these behaviors was mainly focused on the high-frequency components of the intrinsic mode functions.Conclusion The time-frequency characteristics of the human body calf angular acceleration signal can be applied to other kinematic parameters of the lower limbs in order to obtain the movement characteristics of the lower limbs.