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The relation between the surface electromyogram and muscular force.
Author(s) -
MilnerBrown H S,
Stein R B
Publication year - 1975
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1975.sp010904
Subject(s) - motor unit , amplitude , electromyography , surface (topology) , root mean square , anatomy , motor unit recruitment , physics , mathematics , materials science , chemistry , physical medicine and rehabilitation , medicine , optics , geometry , quantum mechanics
1. Motor units in the first dorsal interosseus muscle of normal human subjects were recorded by needle electrodes, together with the surface electromyogram (e.m.g.). The wave form contributed by each motor unit to the surface e.m.g. was determined by signal averaging. 2. The peak‐to‐peak amplitude of the wave form contributed to the surface e.m.g. by a motor unit increased approximately as the square root of the threshold force at which the unit was recruited. The peak‐to‐peak duration of the wave form was independent of the threshold force. 3. Large and small motor units are uniformly distributed throughout this muscle, and the muscle fibres making up a motor unit may be widely dispersed. 4. The rectified surface e.m.g. was computed as a function of force, based on the sample of motor units recorded. The largest contribution of motor unit recruitment occurs at low force levels, while the contribution of increased firing rate becomes more important at higher force levels. 5. Possible bases for the common experimental observation that the mean rectified surface e.m.g. varies linearly with the force generated by a muscle are discussed. E.m.g. potentials and contractile responses may both sum non‐linearly at moderate to high force levels, but in such a way that the rectified surface e.m.g. is still approximately linearly related to the force produced by the muscle.