NECK MUSCLE AND ELECTROMYOGRAPHY MEASUREMENT

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5.1 INTRODUCTION

The previous chapter presented the development of the smart neck support system SnS 2 and the aircraft cabin simulator. In Chapter 3, the design of the developed SnS 2 was described. In Chapter 5 1 , two experiments, namely a calibration experiment and a validation experiment, were designed to evaluate the developed system. Electromyography EMG method was used to measure sternocleidomastoid SCM muscle stress. In order to objectify the EMG value of SCM muscle at a pre‐defined head rotation angle, the calibration experiment was carried out. The calibration experiment was conducted to find the relationship between defined head rotation angle, gender, duration and the SCM EMG value.

5.2 NECK MUSCLE AND ELECTROMYOGRAPHY MEASUREMENT

The SCM muscle is ‘a paired muscle in the superficial layers of the anterior portion of the neck’. The SCM muscle is responsible for flexion and rotation of the human head Wikipedia, 2010a. Costa et al. 1990 described that the SCM muscle is responsible for head movements that were defined as heterolateral inclination, protraction, extension and flexion. Sommerich et al. 2000 also described that the SCM muscle is responsible for flexion, rotation and lateral bending. Figure 5.1 shows the sternocleidomastoid muscle. 1 This chapter is partly based on the following articles: Tan, C.F., Chen, W. and Rauterberg, M. 2010. The Relationship of head rotation angle and SCM EMG value for the development of AnS 2 . World Congress on Engineering WCE2010, London, U.K., pp. 2082‐2085. Tan, C.F. Chen, W. and Rauterberg, M. 2010. An approach to study the sitting position and neck discomfort of economy class aircraft passenger during air travel. International Conference on Applied Human Factors and Ergonomics AHFE2010, Miami, Florida, USA, Chapter 40, pp. 376‐ 382. Tan, C.F., Chen, W. and Rauterberg, M. 2010. Experimental design for sternocleidomastoid muscle stress measurement. 7th International Conference on Methods and Techniques in Behavioral research Measuring Behavior 2010, Eindhoven, the Netherlands, pp. 44‐47. 131 Figure 5.1 The SCM muscle Photograph reprinted from Wikipedia, 2010a. Johnston et al. 2008 studied the electromyography signals from the SCM muscle to determine differences between computer workers with varying levels of neck pain in terms of work stressors, employee strain, EMG amplitude and heart rate response to various tasks. Various studies Ylinen et al., 2003; Bexander et al. 2005; Gabriel et al., 2004; Moon et al., 2003; Lin and Huang, 2008 showed that there is a relationship between EMG activity of the SCM muscle and head rotation. Tilley and Dreyfuss 2001 conducted human factors research about impact of everything in daily life. In their measurement on head rotation angles for man and woman, they defined that the head facing front or in 0° is the most comfortable head position. From 0° to 45° is the easy head rotation angle range and 60° is the maximum head rotation angle. EMG signal is used to measure the myolectrical activity of muscles. Muscle contractions provide an electrical signal and are recorded by EMG Lee et al., 1995; Stegeman et al., 2000. Surface electromyography sEMG has been used in research and clinical applications to measure neck muscles Falla et al., 2002. Based on the literature review, the SCM muscle is a muscle that is related to head rotation and can be measured with EMG. Therefore, the SCM muscle was selected to validate the developed SnS 2 . Sternocleidomastoid muscle 132

5.3 CALIBRATION EXPERIMENT