On-body communication channels are gaining increasing interests as more and more wireless devices are wearable in the fields of medicine, military, and personal communications. This paper presents an experimental investigation of the dynamic features of time-varying on-body channels with continuous movements of human body. Channel response at 10 antenna positions in two dynamic scenarios, walking and standing up and sitting down, have been measured in the anechoic chamber. Based on the statistical analyses of fading duration, a five-state Fritchman model that considers channel dwelling time at a given quality is proposed. Parameters of the Fritchman model are estimated from the measured data. The characteristics of simulated burst channels are in good agreement with the measurements.