Neck muscle control patterns in 3D isometric experiments

Abstract

The better understanding of neuromuscular control of the human neck is of critical importance to understand whiplash injury and neurological movement disorders. Isometric experiments using electromyography (EMG) are an appropriate method to study neuromuscular control patterns of neck muscles. As the human head-neck system is highly complex, it often exerts forces and moments simultaneously during isometric testing. However, literature generally shows no clear distinction between force and moment tasks in isometric experiments and no study tested forces and moments tasks separately in one experiment as the tasks given were ambiguous. The goals of this study were to test force and moment tasks separately in one experiment and analyse the differences in muscle control patterns. 12 healthy male subjects had surface electromyography (EMG) placed bilaterally on 4 neck muscles: sternocleidomastoid, splenius capitis, semispinalis capitis, trapezius. Isometric contractions were performed in a constrained helmet rigidly connected to an overhead loadcell. A new intuitive 3D visual feedback was applied in a neck isometric experiment which assisted subjects in separating force from moment tasks. Subjects performed force and moment tasks through submaximal voluntary contractions (sub-MVCs) in the anterior, posterior, and lateral directions. In a conventional 2DOFs task subjects received 2D feedback which only showed a target point while in a 3DOFs task subjects received an additional DOF feedback which showed a coupled moment in force tasks and a coupled force in moment tasks. Force and moment tasks with 2DOFs and 3DOFs visual feedback were compared. A consistent load coupling pattern was shown in 2DOFs task. Subjects performed force tasks coupled with consistent moment load and moment tasks coupled with force load, for instance, protraction force tasks coupled with extension moment; flexion moment tasks coupled with retraction force. With 3DOFs visual feedback, most subjects nullified the coupled load in the direction where the coupling DOF was displayed (P