Abstract
Mechanical neck disorder is a widespread and non-neurological musculoskeletal condition resulting from modern lifestyles. Presently, the fundamental electrophysiological properties of the motor units of the sternocleidomastoid muscles and the characteristics of the short-term synchronization of the motor unit in patients with neck pain are ambiguous. This study therefore aims to clarify the fundamental electrophysiological properties of the motor units of the sternocleidomastoid muscles in patients with mechanical neck disorder and in asymptomatic individuals. We further investigated whether alterations in the degree of motor unit short-term synchronization occur. The surface electrophysiological signals of the bilateral sternal heads of the sternocleidomastoid muscles of twelve patients with mechanical neck disorder and asymptomatic individuals were detected at 25% of the maximum voluntary contraction during cervical isometric flexion and then decomposed into individual motor unit action potential trains. We found that the patients with mechanical neck disorder showed significantly higher initial and mean firing rates of the sternocleidomastoid muscles and displayed substantially lower motor unit short-term synchronization values compared with the asymptomatic subjects. Consequently, these convincing findings support the assertion that patients with mechanical neck disorder display altered neuromuscular control strategies, such as the reinforcement of motor unit recruitment firing rates in the sternocleidomastoid muscles. The motor units of these patients also revealed neural recruitment strategies with relatively poor efficiency when executing the required motor tasks.
Highlights
Mechanical neck disorder (MND) is commonly considered a widespread and unnerved musculoskeletal condition
479 motor units from asymptomatic individuals and 612 motor units from patients with MND were successfully decomposed into constituent motor unit action potential trains
The results revealed that the identified motor units of the sternocleidomastoid muscles displayed significantly higher initial and mean firing rates in patients with MND
Summary
Mechanical neck disorder (MND) is commonly considered a widespread and unnerved musculoskeletal condition. MND is defined as generalized neck pain and disability without any abnormal anatomical structures or identifiable orthopedic and neurological problems, such as spinal vertebral fracture, exceptional spinal lordosis, spinal spondylosis, spinal osteoarthritis. The symptoms of neck pain, abnormal cervical kinematics, neck muscle weakness and neck-related functional disabilities are the common complaints for patients with MND [1,2,3,4,5,6,7,8,9,10]. The etiology of MND is largely under debate, it is believed that prolonged workloads and poor work postures are potential underlying causes [11,12,13]. Psychosocial risk factors have been reported as potential contributors [14]
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