Muscle fatigue is one of the reason leads to Musculo-Skeletal Disorder(MSD). Automation in today's industries makes human effort very less, but still there are many industries in which human have to do complex and repetitive tasks manually. The society/companies have to pay attention on this issue due to the new laws on penibility or repetitive tasks. The objective of this paper is to experimentally validate a new dynamic muscle fatigue model using electromyog-raphy (EMG) and Maximum voluntary contraction (MVC). A new model is developed by introducing a co-contraction factor 'n' in the Ruina Ma's dynamic muscle fatigue model. The experimental data of ten subjects are used to analyze the muscle activities and muscle fatigue during extension-flexion motion of the arm on a constant absolute value of the external load. The findings for co-contraction factor shows that the fatigue increases when co-contraction area decreases. The dynamic muscle fatigue model is validated using the MVC data, fatigue rate and co-contraction factor of the subjects.