Motor unit potential analysis under submaximal contraction: ADEMG study in normal and radiculopathy subjects

The purpose of this study was to investigate the motor unit potential (MUP) morphology in different degrees of muscle contraction. Fourteen normal volunteers and 8 patients with C7 radiculopathy were included. The extensor digitorum communis muscle was kept in minimal contraction and 5%, 10%, 30% and 50% of maximal contraction under the guidance of strain gauge. Automatic motor unit potential analysis was done by automatic decomposition electromyography for each epoch of muscle contraction in both normal and radiculopathic groups. The results revealed that as muscle contraction increased, the observed MUPs had higher amplitude, rising ratio and firing rate, while the duration became shorter, but no regular change was found in turns reading. These tendencies were found in both normal and radiculopathic groups. This study enhanced the understanding of morphology of MUPs with higher threshold, and proved the usefulness of ADEMG in differentiating normal from cervical chronic radiculopathy condition. It is suggested that the examiner should observe both lower and higher threshold MUPs during clinical needle examination to make diagnosis more accurately.