From: Industrial Health. 2010;48(2):145-53
Frequent material handling activities found in construction work environments put substantial stress on the neck, shoulder, and lower back resulting in pain and discomfort. A number of studies have evaluated the prevalence of different types of musculoskeletal disorders among construction workers. A study of workers compensation claims in Washington (US) show that masonry and residential construction are among the top five industries having the highest risk of injuries. Among Swedish construction workers studied by Holmström et al., 41.1% had neck and shoulder disorders. Building construction is listed among the top ten high-risk industries for musculoskeletal disorders among the Taiwanese working population by Guo et al. Neck and shoulder disorders affect 26.3% of male and 32.1% of female among the Taiwanese construction workers.
Manual material handling activities are an inseparable part of any construction project. Epidemiologically, several review studies have clearly established a strong relationship between work activities requiring forceful arm exertions and the occurrence of neck disorders. Common neck disorders associated with work activities involving forceful arm exertions include degenerative disc disorders such as disc herniation or cervical spondylosis and in some cases more muscle specific disorders such as tension neck syndrome. Even though these disorders are prevalent among construction workers, very few studies have evaluated the underlying pathomechanism.
The purpose of this study was to evaluate physical risk factors (force and posture) associated with neck disorders among construction workers. The role of the major neck muscles during lifting tasks at shoulder height was evaluated biomechanically by studying muscle activity in the cervical region.
The activation of the sternocleidomastoid muscle was significantly affected by the neck posture. At each weight condition, the activation of the sternocleidomastoid muscle was significantly higher at the extended neck posture than the respective neutral and flexed neck postures. The activation of the sternocleidomastoid muscle at the neutral and flexed neck posture was found statistically identical at all weight conditions.
Neck posture significantly affected the activation of upper trapezius muscle along the C4 level. At 25% weight condition the muscle was found most active at the flexed neck posture; however, the values were statistically not significant. At 50% and 75% weight conditions, the muscle was found most active at the flexed neck posture followed by the neutral and extended neck posture. The increase in the activation level with the change in the neck posture from neutral to flexed and from extended to flexed was statistically significant. The increase in the activation level with the change in the neck posture from extended to neutral was statistically not significant.
The activation of upper trapezius muscle along C7 level was also significantly affected by the neck posture. At each weight condition, the muscle was most active at the flexed neck posture followed by the neutral and the extended neck posture. In terms of statistical significance, at 50% weight condition, the activation at the flexed neck posture was significantly higher than the corresponding extended neck posture. At 75% weight condition, the activation at the flexed neck posture was significantly higher than the corresponding extended and neutral neck postures.
The weight lifted substantially affected the contribution of the neck muscles. In the case of the anterior neck muscle (sternocleidomastoid muscle), increased muscle activation with increased weight was significant at extended neck posture and mostly for higher weights (50%, and 75%) at neutral and flexed neck postures. For the posterior neck muscles (upper trapezius muscle) along C4 as well as C7 levels, at all the neck postures, a significant weight-muscle activation relationship was observed. This observed increase in the activation of the upper trapezius muscle along the C7 level with the increase in the weight at the shoulder height is consistent with previous investigations.
Posture had a significant impact on the activation level of the neck muscles. Independent of the weight lifted the sternocleidomastoid muscle was most active at the extended neck posture. The muscle activation at the neutral and flexed neck postures was identical. The upper trapezius muscle was most active at the flexed neck posture followed by the neutral and extended neck postures. However, this neck posture dependent behavior of the upper trapezius muscle was found to be significant only at the higher weight conditions, i.e. while lifting 50% and 75% weights, flexed neck caused substantially higher muscle activation compared to the neutral and extended neck postures. Consistent with findings, previously, increased activation of the upper trapezius muscle along the C7 level, at the flexed neck posture was reported in a number of studies evaluating sitting work postures. Moreover the observed neck posture and muscle-activation trend is in agreement with the muscle force-length relationship i.e. lower activation at shorter length and higher values at increased length.
The upper trapezius muscle, especially along the C7 level, has been widely studied in occupational investigations to evaluate neck and upper extremity disorders. To the authors knowledge no previous study evaluating occupational tasks or forceful arm exertions has reported the activities of the sternocleidomastoid muscle and the upper trapezius muscle in the cervical region. While evaluating neck disorders, understanding the activation of these muscles is vital, as they are bigger (surface) muscles in the neck region and anatomically couple the shoulder to the skull. Such an anatomical orientation may require these muscles to support the shoulder during forceful arm exertions. In confirmation with the authors claim, the results of this study clearly show that, similar to the upper trapezius muscle along the C7, the activation of the sternocleidomastoid muscle and the upper trapezius muscle in the cervical region was sensitive to the lifting weight as well as neck posture.
Overall, the results of this study indicate that the neck muscles play an active role during lifting and holding tasks at shoulder heights. While translating EMG activation of the neck muscles into physical risk factors associated with neck disorders, it is important to understand the possible musculoskeletal disorders pathways. Armstrong et al. presented a conceptual model describing the pathways involved in the pathogenesis of cumulative neck and upper limb musculoskeletal disorders. During work activities, the internal forces acting upon the musculoskeletal system require a response by the body. The response could be physiological or biomechanical in nature e.g. increased circulation, local muscle fatigue etc. The cumulative work activities could require continued or excessive response, which might affect the body’s ability to deal with further responses. With the repetition and/or accumulation of this phenomenon over the time, the reorganization or the regeneration process of the body tissue might be affected, causing structural tissue deformation.
Routine construction work requires lifting objects to shoulder height repetitively. The sustained activity in neck muscles during these tasks can be linked to (1) reduced blood flow, (2) repetitive loading of tendons, (3) rupture of the muscle’s z-discs, and (4) contractile forces acting on the cervical spine. The repetitive loading of the muscles and tendons has been associated with muscle specific neck disorders such as tension neck syndrome, while that of cervical vertebrae has been associated with degenerative disorders such as disc herniation and cervical spondylosis. Thus active contribution of the neck muscles during the lifting and holding of heavy objects at shoulder height could be probable risk factors associated with prevalent neck disorders among construction workers.
Considering the inherent association of lifting tasks with the construction profession, alternative material e.g. light-weight concrete blocks, pre-blended mortar and grout mix1, methods, and tools (Vacuum lifters) could be used to minimize the potential of neck injuries among construction workers. Future studies could be performed to find alternative construction work strategies and also to validate existing interventions.
In summary, this study concludes that lifting and holding weights at shoulder height result in increased activity in the superficial neck flexors and upper trapezius which may be a source of neck musculoskeletal disorders prevalent among construction workers.
