Torque-EMG-velocity relationship in female workers with chronic neck muscle pain
From: Journal of Biomechanics. 2008 May 5
The present study investigated the effect of chronic neck muscle pain (defined as trapezius myalgia) on neck and shoulder muscle function during concentric, eccentric and static contraction. Forty-two female office workers with chronic neck muscle pain and 20 healthy matched controls participated. Isokinetic and static maximal voluntary shoulder abductions were performed in a Biodex dynamometer, and electromyography obtained in the trapezius and deltoideus muscles. Muscle thickness in the trapezius was measured with ultrasound. Pain and perceived exertion were registered before and after the dynamometer test. The main findings were that shoulder abduction torque and trapezius electromyography amplitude were significantly lower in chronic neck muscle pain compared with healthy matched controls. Deltoideus electromyography and trapezius muscle thickness were not significantly different between the groups. While perceived exertion increased in both groups in response to the test, pain increased in chronic neck muscle pain only. In conclusion, having chronic neck muscle pain was associated with decreased strength capacity and lowered activity of the painful trapezius muscle. The most consistent differences-in terms of both torque and electromyography were found during slow concentric and eccentric contractions. Activity of the synergistic pain free deltoideus muscle was not significantly lower, indicating specific inhibitory feedback of the painful trapezius muscle only. Parallel increase in pain and perceived exertion among chronic neck muscle pain were observed in response to the maximal contractions, emphasizing that heavy physical exertion provokes pain increase only in conditions of chronic neck pain due to myalgia.
