Modelling relative masseter force from surface electromyograms during mastication in non-human primates.
The purpose was to analyse the relation between masseter electromyograms (EMGs) and relative masseter force during the power stroke of mastication. The electromyographic activity of the masseter was characterized by recording from bipolar surface electrodes placed over the superficial portion of the muscle; relative masseter force was estimated by characterizing surface bone strain along the lateral aspect of the zygomatic arch. The subjects were six adult macaques and one adult baboon. Masseter EMGs were quantified by r.m.s. analysis of the raw digitized EMG. The length of the time interval (the time constant) during which the r.m.s. values were calculated was repeatedly altered so as to determine which time constant was optimal for producing an EMG-derived waveform that best mimicked relative masseter force during the near-isometric phase of muscle contraction. The data indicate that between subjects this time constant varied from 35 to 72 ms, with an overall median of 42 ms and a grand mean of 49 ms. The use of a 42-ms time constant for all of the subjects resulted in an average latency between the masseter EMG waveform and relative masseter force of about 30 ms during the latter portion of the power stroke of mastication. This analysis provides, as a first approximation, an empirical basis for modelling relative jaw-muscle force using surface EMGs recorded during that portion of the power stroke of mastication when the jaw-closing muscles are contracting under near isometric conditions.
Hylander
W L
WL
Department of Biological Anthropology and Anatomy, Duke University Medical School, Durham, NC 27710.
Johnson
K R
KR
D000818:Animals; D001732:Bite Force; D003799:Dental Stress Analysis / Q000379:methods*; D004576:Electromyography; D005260:Female; D007537:Isometric Contraction; D008252:Macaca fascicularis; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D008409:Mastication / Q000502:physiology*; D008954:Models, Biological; D009119:Muscle Contraction; D010215:Papio; D011930:Reaction Time; D015050:Zygoma / Q000502:physiology