Investigation of the EMG-angle relationship in the upper-limb muscles during isometric contraction. Mohammad Fazle Rabbi 1* , Nizam Uddin Ahamed 2 , Mahdi Alqahtani 3 , Omar Altwijri 3 , Kamarul Hawari Ghazali 1 , K Sundaraj 4 1 Faculty of Electrical and Electronics Engineering, Universiti Malaysia Pahang, Pekan 26600, Pahang, Malaysia 2 Department of Mechatronic Engineering, Faculty of Manufacturing Engineering, Universiti Malaysia Pahang, Pekan 26600, Pahang, Malaysia 3 Department of Biomedical Technology, College of Applied Medical Sciences, King Saud University, Riyadh 11472, Kingdom of Saudi Arabia 4 Department of Electronics and Computer Engineering, Universiti Teknikal Malaysia Malaka, Melaka 75450, Malaysia Abstract Purpose: The relationship between EMG and elbow angle was investigated to identify the signal characteristics of upper-limb muscles during isometric contraction. The study would improve the current understanding of electrophysiological activities of the human upper limbs, which would aid the development of prosthetic arms for rehabilitation research. Subjects and methods: Ten subjects aged 22.4(±1.5) years participated in this study. The electromyography signals from the biceps brachii muscle were recorded during isometric contraction. The root mean square and mean absolute value of the EMG signals were calculated and evaluated to assess the relationship between the signals and elbow angles. In addition, the force exerted by the upper limb was recorded using a dynamometer to identify more features of the relationship. Results: The results revealed that both the RMS and MAV of the EMG signals are not significantly related with the elbow angle (r 2 =0.70 and 0.21; p=0.075 and 0.43, respectively). In contrast, the force is strongly related to the elbow angle (r 2 =0.88, p=0.017). Conclusion: A stronger electrical signal was generated by the upper-limb muscles with an increase in the angle of the elbow joint, whereas a lower force was obtained with an increase in the elbow joint angle. Keywords: Electromyography, Elbow angle, Rehabilitation. Accepted on October 15, 2016 Introduction The movement of the upper limb is essential for basic human activities, such as lifting an object, typing, writing and throwing. These activities essentially involve motion and muscle action. Using electromyography (EMG) signals, muscle actions can be assessed through an analysis of the electrical signals generated by the muscles. The electrical signal generated by upper-limb muscles can be influenced by various external issues, such as muscle contraction, relaxation, elbow joint angle and muscle force. During isometric contractions, the elbow angle is considered one of the factors of the maximum force generated by muscles in the upper limb. A study of the EMG-angle relationship may provide insights into the activity of muscles at different elbow joint angles, which may be particularly helpful for rehabilitation studies. Several studies have investigated the relationships of upper limb muscles with EMG signals. For example, Doheny et al. investigated the EMG-force relationship of the triceps and biceps muscles during elbow extension and flexion [1]. These authors claim that the EMG-force relationship does not vary markedly between a few selected muscles of the upper limb. The EMG-moment and EMG-pennation angle of the tibialis anterior and triceps muscles of healthy subjects were studied by Roberts and Buchanan [2], and their results indicate a moderate relationship for both the EMG-moment and the EMG-pennation angle. The EMG-torque relationship was investigated by Bouchard et al. [3]: the elbow angle was not specified, and four muscles in the biceps and four muscles in the triceps were investigated. A relationship between SEMG and elbow joint angle was proposed by Wu et al. [4]. Ahamed et al. examined the EMG-time relationship of the biceps brachii muscles during isometric and isotonic contractions [5]. Four different upper-limb motion angles were investigated by Goupura et al., who discovered a relationship between the muscle activities related to daily upper-limb motions [6]. ISSN 0970-938X www.biomedres.info 2393 Biomedical Research 2017; 28 (6): 2393-2397 Biomed Res- India 2017 Volume 28 Issue 6