The increasing use of wireless technology in the Body Area Network (WBAN) system has created a demand for accessible data showing the depth of penetration of electromagnetic waves (EMW) into human tissue and how this varies with the wavelength. This information would be especially useful in medical studies and would aid in the development of WBAN for specific diseases based on a better understanding of the electromagnetic penetration effects. In this paper, we estimate the magnitude of the electric field inside muscle tissue at various depths and with the most important frequencies in medical applications. Moreover, this investigation provides evidence that the penetration of EMW in biological tissue strongly depends on the frequency and thickness of the tissue involved. The method used here is based on an analytical model, and it focuses on the impact of incident plane waves incoming in a lossy medium on muscle tissue using the Method of Moments (MoM). All results are finally validated and compared through Finite Element Method (FEM) computations. The presented study is interesting in view of a practical application of the effects of deep wave penetration.