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The purposes of this study were to (1) examine the effects of different cervicothoracic postures on the stiffness of trapezius muscles and (2) compare the stiffness of the dominant and non-dominant trapezius muscles.

Twenty-one healthy participants joined in this project. After maintaining different cervicothoracic postures for 2 min, MyotonPRO was used to measure the stiffness of the trapezius.

The results showed that (1) the stiffness of trapezius muscles was significantly affected by different cervicothoracic postures. With the increase of neck flexion angle, the stiffness of the trapezius muscles increased (p < 0.05). The muscle stiffness of upper back relaxed was higher than that of upper back upright (p < 0.05). (2) The trapezius muscles on the non-dominant side were stiffer than that on the dominant side (p < 0.05).

Poor cervicothoracic postures will increase the stiffness of upper, middle and lower trapezius muscles. Keeping the neck and upper back upright will keep the muscle stiffness at a low level, so as to reduce the occurrence of neck and shoulder fatigue and pain.

Keywords: cervicothoracic posture, trapezius muscles, stiffness, MyotonPRO

This study investigated the effects of different cervicothoracic postures on trapezius muscle stiffness. The greater the neck flexion angle, the greater the stiffness of the trapezius muscles. The trapezius muscles were stiffer when the upper back was relaxed than when the upper back was upright. The trapezius muscle stiffness of the non-dominant side was higher than that of the dominant side. Therefore, although the use of smartphones cannot be avoided, the upright posture of the neck and upper back should be maintained during use, and the use of smartphones should be suspended at regular intervals to adjust the poor cervicothoracic posture so that the muscles have sufficient time to recover, so as to avoid muscle fatigue and pain.