ABSTRACT CHAFFIN, DON B., MYUN LEE, and ANDRIS FREIVALDS. Muscle strength assessment from EMG analysis. Med. Sci. Sports Exercise. Vol. 12, No. 3, pp. 205–211, 1980. Isometric strength is a useful indicator of a person's capacity to safely perform tasks requiring high physical effort. This paper develops and evaluates a method for the improved assessment of such strength using surface electrode EMG analysis of graded, submaximal exertions. The method is evaluated by having two groups of volunteers each perform repeated isometric elbow flexions while EMG's were obtained from the biceps brachii. Subjects in one group were instructed by a third party to “fake” all exertions at levels between 50% and 75% of that requested by the experimenter. The second group was asked to give full cooperation. The experimenters were “blind” as to which group any one subject belonged until all EMG analyses were complete. The EMG's were evaluated by comparing their rectified amplitudes during a slowly increasing (five second) exertion requirement and a submaximal exertion at a requested 50% MVC level until fatigue, i.e., when the subject no longer could or would retain the requested exertion over a three-second period. The changes in the EMG amplitude during the endurance hold were used to determine the maximum potential EMG and whether the subject was faking or sincere. The changes in the relationship between EMG amplitude and the force of exertion on the progressive exertion requirement along with the estimated maximum EMG allowed the prediction of maximum strength and thus the level at which each subject was exerting. Of the 22 subjects, all 10 fakers and 11 of 12 sincere subjects were correctly identified. A theoretical basis for the method is discussed.