This paper presents two energy-efficient techniques to enhance the channel quality of body channel communication (BCC). From Maxwell's equations, the complete equation of electric field on the human body is obtained to develop the theoretical transmission mechanism of BCC, which consists of a combination of the quasi-static near-field coupling, and surface wave far-field propagation mechanism. Based on the channel analysis, the resonance matching (RM) and contact impedance sensing (CIS) techniques are proposed for the sake of the optimization of electric signal transmission through the human body, which leads to reduce the requirements for BCC transceiver. As a result, 1) the RM gives 4dB channel enhancement with reduced power consumption by BCC transmitter, and 2) the CIS reduces both the linearity and sensitivity requirements of the BCC receiver by 7dB with significant power saving.