The electromyography (EMG) has been used as a resource related to clinical interventions, as well as control of the adjustments resulting from physical training, especially the muscular strength. The muscular electrical activity allows the investigation of which muscles are used in a motion, the level of muscle activation during the course of movement, intensity and duration of muscular demand. Due to the great usefulness of the study of muscle electrical signal and its complex relationship with the force production, both the relation to physiological and non physiological aspects as well as the procedures needed for the collection of EMG signal in isometric and dynamic activity took place this review. Therefore, the EMG signal presents relation with the strength production of the knee extensor muscles. This relationship has been better demonstrated in isometric assessments than in dynamic conditions, what stimulates further scientific production in this area to better understand and explain the relationship of the contraction dynamics, the production of force and changes in EMG signal and improve their applicability not only in the scientific scope, but in clinical tool, since the dynamic activities are similar to the sports gestures and activities of daily living
