The purpose of this study was to investigate the motor units recruitment and muscle fatigue of the Biceps Brachii during Voluntary Isometric Contractions by using Electromyogram. Experiments have been performed for measuring and analyzing the changes of the Rectified EMG Amplitude and IEMG valuse during prolonged exertions at 75%, 50%, 25% MVC. The results were as follows: 1 The Initial REMG Amplitude depended upon the leves of % MVC but the Final REMG Amplitude was not different among the 75%, 50%, 25% MVC. 2. The REMG Amplitude gradually increased with respect try muscle fatigue progression. 3. In case of 75% MVC, The IEMG values increased linerly through single section. 4. In case of 50% MVC, The IEMG values increased non-linearly at 63-72% of the Maximum Contraction Duration through two sections. 5. In case of 25% MVC, The IEMG value increased non-linearly at 41-54% and 78-87% of the Maximum Contraction Duration through three sections.