Abstract
Cervical spinal loads are predominately influenced by activities of cervical muscles. However, the coordination between deep and superficial muscles and their influence on the spinal loads is not well understood. This study aims to document the changes of cervical spinal loads and the differential contributions of superficial and deep muscles with varying head postures. Electromyography (EMG) of cervical muscles from seventeen healthy adults were measured during maximal isometric exertions for lateral flexion (at 10°, 20° and terminal position) as well as flexion/extension (at 10°, 20°, 30°, and terminal position) neck postures. An EMG-assisted optimization approach was used to estimate the muscle forces and subsequent spinal loads. The results showed that compressive and anterior-posterior shear loads increased significantly with neck flexion. In particular, deep muscle forces increased significantly with increasing flexion. It was also determined that in all different static head postures, the deep muscle forces were greater than those of the superficial muscle forces, however, such pattern was reversed during peak efforts where greater superficial muscle forces were identified with increasing angle of inclination. In summary, the identification of significantly increased spinal loads associated with increased deep muscle activation during flexion postures, implies higher risks in predisposing the neck to occupationally related disorders. The results also explicitly supported that deep muscles play a greater role in maintaining stable head postures where superficial muscles are responsible for peak exertions and reinforcing the spinal stability at terminal head postures. This study provided quantitative data of normal cervical spinal loads and revealed motor control strategies in coordinating the superficial and deep muscles during physical tasks.
Highlights
The normal spinal loads are mainly maintained and regulated by a complex multi-layered cervical muscular system during daily activities involving head movements
This study aimed to examine the changes of spinal loads and the corresponding contributions of the superficial and deep neck muscles in controlling the cervical spine during static peak efforts and changing head postures
The results showed that the compressive loads and the anterior-posterior shear loads were significantly increased with increasing neck flexion angle
Summary
The normal spinal loads are mainly maintained and regulated by a complex multi-layered cervical muscular system during daily activities involving head movements. Superficial muscles are traditionally assumed to be the motion actuator, whereas deep muscles help to fine tune the curvature and hold an upright posture of the cervical spine [1]. It has been documented that the activation of cervical muscles, either for motion production or providing stability, will inevitably increase the loading of the spine [2]. A better understanding of spinal loads as contributed by muscle activations under environmental challenges would assist in the diagnosis and rehabilitation in preventing the development of postural induced spinal disorders. All muscles are predominately viewed as identical elements when functioning in neutral posture in those models, and the different characteristics of the superficial and deep muscles and their roles in regulating the spinal loads at different head postures still lacks empirical evidence
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