Effects of different movement directions on electromyography recorded from the shoulder muscles while passing the target positions Yoshinari Sakaki a,d , Fuminari Kaneko b,⇑ , Kota Watanabe c , Takuma Kobayashi c , Masaki Katayose b , Nobuhiro Aoki b , Eriko Shibata a , Toshihiko Yamashita c a Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan b Second Division of Physical Therapy, School of Health Sciences, Sapporo Medical University, Sapporo, Japan c Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan d Department of Rehabilitation, Hitsujigaoka Hospital, Sapporo, Japan article info Article history: Received 29 January 2013 Received in revised form 7 August 2013 Accepted 28 August 2013 Keywords: Rotator cuff Shoulder joint Electromyography Movement direction Motion analysis abstract Purpose: We compared electromyography (EMG) recorded from the shoulder joint muscles in the same position for different movement directions. Methods: Fifteen healthy subjects participated. They performed shoulder elevation from 0° to 120°, shoulder depression from 120° to 0°, shoulder horizontal adduction from À15° to 105°, and shoulder hor- izontal abduction from 105° to À15°. The target positions were 90° shoulder elevation in the 0°, 30°, 60°, and 90° planes (0°, 30°, 60°, and 90° positions). EMG signals were recorded from the supraspinatus (SSP) muscle by fine-wire electrodes. EMG signals from the infraspinatus (ISP), anterior deltoid, middle deltoid, and posterior deltoid muscles were recorded using active surface electrodes. Results: During elevation and horizontal abduction, the SSP showed significantly higher activity than that shown during depression and during horizontal adduction in the 0°, 30°, and 60° positions. During ele- vation, the ISP showed significantly higher activity than during depression and during horizontal adduc- tion in the 90° position. During horizontal abduction, the ISP showed significantly higher activity than during depression in the 90° position. Conclusions: When the movement tasks were performed in different movement directions at the same speed, each muscle showed characteristic activity. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Shoulder surface muscles include the deltoid muscle and the pectoralis major muscle, which enable the execution of shoulder movements. The rotator cuff acts to stabilize the glenohumeral joint in various limb positions (Kronberg et al., 1990; Inman et al., 1996; Wuelker et al., 1998). It was reported that in shoulder joint diseases such as subacromial impingement, frozen shoulder and thrower’s pathologic shoulder, the function of the rotator cuff is relatively less than the function of the surface muscles (Williams and Kelley, 2000). Therefore, to understand the mechanisms underlying shoulder joint diseases and to provide the optimal rehabilitation for rotator cuff, a thorough elucidation of the func- tional characteristics of the rotator cuff is necessary. The functional characteristics of the rotator cuff have been examined in the previous studies using techniques such as a cadav- eric shoulder, electromyography, X-rays, and magnetic resonance imaging (Kronberg et al., 1990; Inman et al., 1996; Wuelker et al., 1998). It was reported that the supraspinatus (SSP) muscle contributes to shoulder abduction movement (Howell et al., 1986; Otis et al., 1994; Alpert et al., 2000), and that the infraspinatus (ISP) muscle pulls the head of the humerus into the glenoid fossa (Alpert et al., 2000; Yanagawa et al., 2008). These studies only focused on the rotator cuff’s functional char- acteristics in a single movement direction. However, the shoulder’s movements in daily living and sports activities are multidirec- tional, and the movement direction that passes through the same position in space is generally not one direction. In the previous studies, it was not clarified whether shoulder muscle activity dif- fers during different movement directions when the upper limb is in the same position. The purpose of the present study was to record electromyography from the shoulder joint muscles in the same position for different movement directions. 2. Methods 2.1. Subjects Fifteen healthy male subjects (aged 23.1 ± 1.2 years) who re- ported that they did not exercise regularly participated. The study 1050-6411/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jelekin.2013.08.010 ⇑ Corresponding author. Address: West 17, South 1, Chuo-ku, Sapporo City, Japan. Tel.: +81 11 611 2111. E-mail address: f-kaneko@sapmed.ac.jp (F. Kaneko). Journal of Electromyography and Kinesiology 23 (2013) 1362–1369 Contents lists available at ScienceDirect Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin