Multi-channel array EMG in chronic neck-shoulder pain

Chronic muscular pain has become an important problem, affecting a considerable part of the working population in the industrialised countries. Chronic muscular pain is a multifactorial problem and comprises a range of conditions that are not all clinically well-defined. Subjective symptoms include constant muscle pain, muscle fatigue and/or stiffness, and radiating pain. Identified risk factors for the development of chronic pain in the neck-shoulder region include exposure to awkward posture, repetitious movements, low level static contractions and high force demands. Beside these physical factors, psychosocial risk factors such as stress, high job demands and low vocational satisfaction play an important role. A variety of individual factors such as age, body mass index and perception of work load can contribute to the development of chronic pain as well. Several pathophysiological models, explaining the mechanisms that underlie the development of chronic pain, have been proposed. The vicious circle model predicts a positive feedback loop consisting of muscle pain that via nociceptors activates the γ-motoneuron system that projects to the α-motoneuron, thereby activating the muscle, which in turn leads to increased muscle pain. The pain adaptation model suggests a task-dependent increased antagonist activity and decreased agonist activity, thereby reducing painful movements. The Cinderella hypothesis suggests that muscle fibres of low-threshold motor units (MUs) are getting damaged in chronic pain cases because of continuous activation and lack of sufficient muscle relaxation. These models have in common that they predict changes in motor control. However, the models propose different working mechanisms and consensus on the nature of the changes in motor control is lacking. A better understanding of the underlying mechanisms is an important prerequisite for development of effective treatment methods. Model-based experimental studies assessing motor control in chronic pain cases may provide more insight into these mechanisms......