NONINVASIVE APPROACH TO MOTOR UNIT CHARACTERIZATION - MUSCLE STRUCTURE, MEMBRANE DYNAMICS AND NEURONAL CONTROL

The standard surface EMG reflects the compound activity of a high numb er of motor units which is finally due to its low spatial resolution i n the detection of the potential distribution on the skin surface. The refore, detailed information about the structural and functional chara cteristics of the muscle consisting of populations of motor units, lik e the functional anatomy, the excitation spread or the innervation pat tern cannot be obtained from the standard surface EMG. A never noninva sive EMG-procedure with high spatial resolution (HSR-EMG) allows in co ntrast to the standard surface EMG even the detection of the single mo tor unit activity. In this way, the noninvasive determination of detai led information about the muscle structure, the membrane dynamics and the neuronal control becomes possible. First applications of the HSR-E MG have shown that especially the noninvasively measured conduction ve locity of the excitation is highly affected by physiological details, like the muscle temperature, the relative muscle fibre diameter or inh omogeneities in the connective tissue forming part of the volume condu ctor around the muscle. From the results of the HSR-EMG investigations it can be concluded that the information about the structural and fun ctional characteristics of the muscle as well as a deeper insight in t he active state of the muscle is essential for a correct interpretatio n of the standard surface EMG. (C) 1997 Elsevier Science Ltd.