Introduction A traditional problem faced by clinicians attempting to objectively measure musculoskeletal disorders such as low back pain, where there is often primarily soft tissue involvement, is that psychosocial factors (e.g., fear-avoidance, secondary gain) frequently influence the experience/reporting of pain. Nevertheless, there is still a great need for the quantification of physical function, with appropriate criteria in place, in order to help assess both physical impairment and therapeutic endpoint following treatment. One such potentially objective measure is surface electromyographic (sEMG) recordings during purposeful muscular activity and resting states. The present randomized controlled study assessed the potential validity of a new sEMG approach—the comprehensive muscular activity profile (CMAP)—by addressing the following question: can the CMAP accurately document whether a subject is exerting appropriate muscular effort during range-of-motion and lifting testing, or is submaximum effort being exerted? Methods Eighty healthy volunteers were randomly assigned to either: (1) an instruction group encouraging maximum effort on the tests; or (2) an instruction group encouraging “faking” and not putting in maximum effort on the tests. Therapists, who then administered the CMAP protocol (range-of-motion and lifting tests), were kept blind to subject group assignment. They were also asked to complete a rating scale evaluating whether subjects were exerting maximum effort after all the tests were completed. Results In differentiating between the two instruction groups, the CMAP demonstrated high levels of sensitivity [predicting maximum effort on all tests (ranging from 84.6 to 94.9%)]. In contrast, the sensitivity of the therapists’ ratings was much lower (ranging from only 72.5 to 80.0%). Most importantly, when the CMAP data and therapists’ ratings were combined, logistic regression analyses revealed high rates of sensitivity (94.4–97.2%), specificity (84.6–92.3%), and overall classification (90.7–93.3%). Conclusion The results of this study demonstrate the potential utility of the CMAP, combined with therapist ratings, as a valid method of objectively quantifying subject muscular performance and effort during lumbar range-of-motion and lifting tasks.