Abstract
Neck pain is prevalent among computer users and it is postulated that it may be due to continuous firing of single motor units. This study describes the activation pattern of motor units in the trapezius muscle of healthy subjects and the following questions are examined: i) Do some persons not completely relax their neck muscles and does such a motor behavior induce constant activity of single motor units? ii) Does auditory attention or fast repetitive finger movement induce constant activity of single motor units in the trapezius muscle? Three male and three female subjects performed three tasks (resting, tapping, typing) during three minutes. Three channel intramuscular EMG was registered from the descending part of the trapezius muscle using four wire electrodes. The three minute recordings of each session were divided into ten second segments which were separately analyzed with the MAPQuest program. MAPQuest allows the complete decomposition using a modified Viterby algorithm. The results showed that the trapezius muscle was active in one subject while relaxing, in two subjects while inputting, and in five subjects while tapping. Long lasting single motor unit firing was observed in two subjects while inputting and in one subject while tapping. We conclude that in the trapezius muscle continuous motor unit firing may be induced by typical computer work and that its intensity depends both on individual and task characteristics. The measurement period was too short to draw definite conclusions and, for further discussion, it is necessary to evaluate longer periods.
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