Cross sectional muscle physiology studyThe effects of isometric contraction of shoulder muscles on cervical multifidus muscle dimensions in healthy office workers
Introduction
Neck pain is considered as one of the most prevalent problems of modern society (Fernández-de-las-Peñas et al., 2011) causing both disability and functional impairment in office workers (Leijon et al., 2004). It has been reported that more than 34% of people have experienced some kind of neck pain during their lives (Straker et al., 2011).
Several biomechanical and physiological changes have been recorded in patients suffering from neck pain, including reduced strength of deep and superficial neck muscles (Elliott et al., 2008, Falla et al., 2004, Ylinen et al., 2004, O'Leary et al., 2011). Deep cervical muscles are accountable for head and neck stability in both static and dynamic postures (Falla et al., 2007). This muscular stability plays an essential role in preventing strains and injuries to neck structures (Wilke et al., 1995). The Cervical multifidus muscle (CMM) is regarded as a deep neck extensor muscle providing such stability (Wilke et al., 1995). Physiological changes in the CMM has previously been reported in patients with neck pain (Fernández-De-Las-Peñas et al., 2008), in addition to a disturbance to the stability of the cervical spine as a result of CMM weakness. Physical exercises are well recognized in remedying instability and muscular weakness (Kay et al., 2005). However, none of the recommended exercises specifically activates CMM, and at present, we have too little information on these various movements activating CMM effectively. Such movements are designed to prevent muscular weakness, while assisting with the strengthening of these.
It is assumed that the function of CMM is very similar to that of the lumbar multifidus muscle (LMM). Both muscles have a unique feed-forward role in providing intersegmental stability (Anderson et al., 2005, Ward et al., 2009). LMM activity has been reported during the movements of both lower and upper extremities documented before and after an arm flexion task (Moseley et al., 2002), in addition Danneels et al. have shown that the LMM cross-sectional area (CSA) increases by resistance exercises of the lower extremities (Danneels et al., 2001). Therefore, the expectation is that CMM is activated by movements causing lumbar multifidus muscle activation in tasks performed by the upper extremities, if CMM is functionally considered equal to LMM.
To study the functions of the cervical muscle, various methods such as electromyography (EMG), muscle functional magnetic resonance imaging (mfMRI) and ultrasonography have been used, among which ultrasonography is non-invasive and highly comparable to MRI. It has been also shown to be a feasible and reliable method to evaluate the dorsal neck muscles dimensions during muscular contraction (Javanshir et al., 2011, Kiesel et al., 2007, Rezasoltani et al., 2002). The high reliability of CMM ultrasonography has been reported at the level of C4 in the resting position (Kristjansson, 2004). In a more recent study, it was revealed that the CMM thickness increased during different levels of isometric cervical extension (Lee et al., 2007).
While considering the function of CMM, this study was implemented with the objective of examining the effects of isometric contraction of shoulder muscles on the dimensions of cervical multifidus muscle as measured by ultrasonography.
Section snippets
Participants
A total of 23 healthy male office workers (right handed; mean age: 24 ± 4 years) voluntarily participated in this cross sectional study. Participants were excluded if they had any history of neck pain in the last year, cervical trauma, or history of spinal surgery. The procedure was explained to the participants prior to the study and informed consents were obtained from those who agreed to participate. The study was approved by the Research Ethics Board of the Faculty of Rehabilitation, Shahid
Statistical analysis
A 5-by-2-by-6 repeated measures analysis of variance (ANOVA) with force (0, 25, 50, 75 and 100% MVC), side (the right and the left CMM) and direction (6 movement directions of the shoulder joint) was used to determine the main effects and interactions of the three, within factors using SPSS software (version 16; SPSS Inc., Chicago, USA). Intraclass coefficient of correlation (ICC), standard error of measurement (SEM) and smallest detectable difference (SDD) were used to determine relative and
Results
A high to very high level of reliability was determined with ICC ranging from 0.75 to 0.91, SEM ranging from 0.04 to 0.06 and SDD ranging from 0.11 to 0.17 for APD, and ICC ranging from 0.70 to 0.92, SEM ranging from 0.06 to 0.11 And SDD ranging from 0.17 to 0.30 for LD.
The results of the present study demonstrated that the CMM thickness was significantly increased (P < 0.01) while the lateral dimension and the shape ratio of the muscle were decreased significantly (P < 0.01) by isometric
Discussion
In the present study, we have evaluated the effects of isometric contraction of shoulder muscles on the CMM dimensions. The results of this study provide evidence of an increase in the CMM thickness during isometric contraction of shoulder muscles in all movement directions. This is in agreement with previous studies that reported isometric head extension results in an increased thickness of CMM (Lee et al., 2007). A possible explanation for this finding is that deep fibers of CMM contracted in
Limitations and future recommendations
Given the fact that the isometric contraction of shoulder muscles is a static task, future studies may be required to evaluate the effects of a dynamic task similar to the performance of activities of daily living on the dimensions of CMM. We failed to include females as the majority of office workers who agreed to participate in the study were males. A comparative study in the future is of interest to evaluate the differences between CMM responses to shoulder muscle contraction in both
Conclusion
This study has revealed that isometric contraction of shoulder muscles lead to changes in CMM dimensions regardless of the direction of force. This may indicate that isometric contraction of shoulder muscles activates CMM which has an impact on the function of the cervical spine. The result of this study may help those interested in designing specific exercises to prevent weakness in deep cervical muscles or strengthen them in order to enhance the cervical spine stability.
Conflict of interest
No conflict of interest is declared.
Acknowledgment
We would like to thank all office workers who voluntarily participated in the present study. We would also like to sincerely thank Ms Roghayeh Dehghani for her continuous support in designing and writing the software for the present study.
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