This paper presents a simple, yet realistic and accurate model for signal transmission through the human body. The model is developed for intra-body communications, covering the range 100 KHz-50 MHz. To gain a deeper insight about the human body gain profile, biological parameters collected from statistical studies, were utilized when deriving the representative circuit model. The resulting model is the first to consider human age and weight as input parameters determining the models' response, and hence the different impedance values. Simulation results compared with prior work using conventional modeling approaches, as well as, with previously published experimental results, confirm the models' accuracy.