Optimal Normalization Tests for Muscle Activation of the Levator Scapulae, Pectoralis Minor, and Rhomboid Major: An Electromyography Study Using Maximum Voluntary Isometric Contractions

Abstract Objective To identify maximum voluntary isometric contraction (MVIC) test positions for the deeper-lying scapulothoracic muscles (ie, levator scapulae, pectoralis minor, rhomboid major), and to provide a standard set of a limited number of test positions that generate an MVIC in all scapulothoracic muscles. Design Cross-sectional study. Setting Physical and rehabilitation medicine department. Participants Healthy subjects (N=21). Interventions Not applicable. Main Outcome Measures Mean peak electromyographic activity from levator scapulae, pectoralis minor, and rhomboid major (investigated with fine-wire electromyography) and from upper trapezius, middle trapezius, lower trapezius, and serratus anterior (investigated with surface electromyography) during the performance of 12 different MVICs. Results The results indicated that various test positions generated similar high mean electromyographic activity and that no single test generated maximum activity for a specific muscle in all subjects. The results of this study support using a series of test positions for normalization procedures rather than a single exercise to increase the likelihood of recruiting the highest activity in the scapulothoracic muscles. Conclusions A standard set of 5 test positions was identified as being sufficient for generating an MVIC of all scapulothoracic muscles: seated T, seated U 135°, prone T–thumbs up, prone V–thumbs up, and supine V–thumbs up. A standard set of test positions for normalization of scapulothoracic electromyographic data that also incorporates the levator scapulae, pectoralis minor, and rhomboid major muscles is 1 step toward a more comprehensive understanding of normal and abnormal muscle function of these muscles and will help to standardize the presentation of scapulothoracic electromyographic muscle activity.