A new hybrid analytical-numerical method is derived that allows the fast and accurate computation of the specific absorption rate (SAR) induced inside a plane geometry fat-muscle tissue by exposure to shortwave diathermy induction coil. The electric field inside each layer of the medium is explicitly provided as combination of Hankel functions starting from the exact integral expressions for the electromagnetic (EM) field generated by a current-carrying loop located horizontally above a two-layered earth. The radial distribution of the SAR and the peak heating as a function of the frequency are computed by applying the proposed model and the zero-order model based on the quasi-static field assumption. Numerical results show that the zero-order model leads to over-estimate the SAR up to more than 20%.