Usefulness of surface electromyography of hand muscles in the assessment of myoelectric parameters changes due to repetitive manual tasks

The aim of this project was to investigate the possible role of sEMG in the diagnosis of Carpal tunnel syndrome (CTS). The study group consisted of 37 subjects, of whom 14 (control group) were not employed in manual tasks and 23 (exposed) were engaged in repetitive and forceful manual tasks. Of the 23 exposed workers, 10 reported CTS symptoms, whereas all the subjects of the control group resulted asymptomatic. The surface electromyography signal was recorded from the abductor pollicis brevis muscle, using different levels of isometric contraction: 20% and 50% of the maximum voluntary contraction (MVC), respectively. The initial values and rate of change of the average rectified value (ARV), mean power spectral frequency (MNF) and conduction velocity (CV) were calculated. Moreover the study protocol included clinical evaluation and electrodiagnostic study of the median nerve. Data from the exposed and control group were compared. Statistically significant differences between the two groups were found for ARV initial value and for CV and MNF rate of change at 50% MVC. These parameters resulted lower in the exposed group, with the lowest values among symptomatic subjects. Possible explanations may be the loss of motor units, particularly affecting the fast and fatigable type II muscle fibers, involved in the myoelectric manifestation of fatigue. In conclusion, this technique was able to show different myoelectric patterns and manifestations of fatigue between subjects exposed and nonexposed to manual intensive work, suffering or not suffering from CTS.