In this study, Surface electromyography (sEMG) signal is used to evaluate the biceps brachii muscle by estimating the muscle fatigue during isometric contraction. Sample of eight males performed isometric action using the biceps brachii muscle with different levels of force and loads. The surface electromyography (sEMG) signal was recorded by the MP 100 EMG system (BIOPAC Systems, California) for 120 seconds intervals without rest in order to achieve the fatigue, the recorded signals were analysed to find parameters in the sEMG that could estimate the muscle fatigue. The median frequency (MDF) of the power spectral density (PSD) and the root mean square value (RMS) were used as spectral and temporal variables to assess fatigue. Decreasing trend was found for (MDF) with time as the biceps muscle fatigues, while the (RMS) did not express consistent tendency with the fatigue process. Least square regression line model were adopted for each variable to form an index for fatigue assessment. The subjects were classified according to this index at the three loads to check the ability of the MDF to evaluate the muscular fatigue for each individual.