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Designing for Head and Neck Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
Neck flexion motion is naturally more limited than the extension motion. In other words, you can look up more fully than you can look down (Palastanga et al., 2002, p. 520). In flexion, the sternocleidomastoid muscles on both sides of the neck act together with shortening contractions to bring the chin toward the chest (Basmajian & De Luca, 1985, p. 469). Recall the naming conventions for muscles. The sternocleidomastoid muscle originates from both the sternum and clavicle (cleid in Greek) and inserts on the mastoid process of the skull. With these origins and a head/neck flexion action, the sternocleidomastoid muscles are the muscles most likely to come into contact with a collar or other wearable product encircling the neck. Many smaller deep muscles also assist with neck flexion (Figure 3.15, center left). With neck extension, the R and L trapezius (Moore et al., 2011, p. 309), at the back of the neck, and the slightly deeper R and L splenius capitis (Figure 3.15, upper) act along with several smaller and deeper muscles to tip the head backward (Basmajian & DeLuca, 1985, pp. 468–469). The trapezius and splenius capitis may also press against a product worn on the neck. Muscles producing these flexion or extension motions (agonists) act bilaterally, with shortening contractions. For example, when the muscles in the back (posterior) of the head and neck are shortening in extension (agonists), the flexor muscles in the anterior neck (antagonists) contract with lengthening contractions to control the motion, or else relax and stretch.
Repeatability of electromyography normalization of the neck and shoulder muscles in symptomatic office workers
Published in International Journal of Occupational Safety and Ergonomics, 2018
Montakarn Chaikumarn, Nuttika Nakphet, Prawit Janwantanakul
The study and focus on the musculoskeletal function of the neck and shoulders require high reliability for EMG normalization [22]. Previous studies have shown high levels of reliability of SEMG for the assessment of the upper trapezius and sternocleidomastoid muscle in healthy subjects during functional tasks [30–32]. One study into the cervical paravertebral muscle during sustained isometric contraction discovered the EMG assessment during sustained isometric contractions to be highly reliable for both the sitting and prone positions within a healthy population [33]. Recently, Marker et al.’s [34] investigation of upper trapezius muscle activity in office workers also found good reliability. Despite these previous studies on the reliability of SEMG in the analysis of the neck and shoulder musculature, most were performed in healthy subjects [30–33,35]. Therefore, there is a need to examine the reliability of SEMG on the variables of amplitude and spectral frequency in the neck and shoulder muscles of symptomatic subjects. In addition, no reliability studies have been investigated in symptomatic office workers. Therefore, in this study we determined the reliability of the EMG normalization of the neck and shoulder muscles in symptomatic office workers. The MVIC method was used for the following muscles: cervical erector spinae, upper trapezius, lower trapezius and anterior deltoid.