Alterations in electromyograms due to inactivity-induced atrophy of the human muscle

Regarding disuse atrophy, numerous investigations attempting to determine typical alterations of EMG measured with concentric needle electrodes have led to mutually inconsistent results concerning amplitude, duration, polyphasy, and number of spikes of motor unit action potentials. Our study comprises 21 patients with one-sided atrophy of m. quadriceps caused by immobilization and a control group of 19 healthy persons. Sufferers of myogenic, neurogenic or haemostasiological diseases as well as all persons on medication were excluded. Quantification of atrophy was performed by myosonography and measuring of circumferences. Both methods proved to be equivalent and more precise than computed tomography. Nearly all values of measurements in patients and in the control group remained within the normal range. But comparing EMG of atrophic m. vastus lateralis with the non-immobilized muscle of the other side revealed statistically significant differences in amplitude (14.1% higher in the atrophic muscle), duration (6.5% longer), number of phases (+13.2%) and spikes (+13.9%). In the healthy muscles of the control group we found no significant differences between dominant and non-dominant legs. Partly consistent and partly contradictory results in other studies may be explained by: a) too few cases examined, b) absence of control groups and/or c) omission of comparisons between right and left legs, but also d) by differences in applied normal values and e) by decreased innervation due to pain, swelling, contractures or arthrodeses. A very important factor was f) the duration of immobilization and g) the time elapsed between the end of immobilization and the examination.