Elbow extension using anterior deltoids and upper pectorals in spinal cord-injured subjects

Abstract

Objective: Surface electromyography was used to identify muscles active in isometric elbow extension in spinal cord-injured (SCI) patients. Design: Tetraplegic subjects participated in this cohort study aimed at identifying some of the muscles that are active during isometric elbow extension. Setting: Regional Spinal Cord Injury (SCI) Center. Patients: The patients had to have a C6 motor level on the right side (wrist extensor ≥3/5) with 0/5 or 1/5 elbow extensor muscle power. Of 32 patients who could be contacted by telephone, 6 eventually were able to make it to the SCI center for testing. Measurements: The patients performed a series of isometric elbow extension contractions of 25%, 50%, and 75% of maximum voluntary contraction (MVC) as measured by a force transducer. Surface electromyography (EMG) of the right elbow extensor, anterior deltoid, and upper pectoral muscles was measured using the root mean square (rms) of the amplitude of the motor unit activity as the parameter of muscle activity. Statistical analyses were performed using a repeated analysis of variance (ANOVA) with Tukey post-hoc HSD for each percentage of MVC. Results: For each muscle tested, there was significantly ( p < 0.05) greater rms activity for each percentage of MVC except between 50% and 75% MVC of the elbow extensor muscle. However, the elbow extensor muscle had minimal EMG activity when compared with the amplitude of the rms activity of the anterior deltoid and upper pectoral muscles for each percentage of MVC. Conclusion: The results of the study suggest that the anterior deltoid and the upper pectoral muscles exert an isometric elbow extension force for C6 quadriplegic patients.