title: Task-dependence of jaw elevator and depressor co-activation.
abstract: Elevator muscle activity per unit bite-force has been shown to be higher in chewing than in isometric biting. We tested the hypothesis that surplus elevator activity is evoked in response to a possible co-activation of jaw-opener muscles during the masticatory power stroke. In 32 subjects, digastric and bilateral masseter and temporalis activities were recorded during unilateral chewing of test foods, isometric biting on a force transducer, and during balancing of the jaw against maximum effort of depressor muscles. During elevator peak effort in chewing, the digastric activity was 113% higher than during peak effort in isometric biting. Comparison of balancing and chewing trials revealed that a 6% increase of elevator activity would suffice to compensate for this increased depressor action. Elevator activity in chewing, however, was up to 130% higher than in clenching. We conclude that depressor counteraction could have only a minor influence on the generation of surplus muscle activity in chewing.
authors.affiliation: Department of Prosthodontics, University Dental Clinic, University of Erlangen-Nürnberg, Glückstrasse 11, D 91054 Erlangen, Germany. peter.proeschel@rzmail.uni-erlangen.de
authors.forename: P A
authors.initials: PA
authors.lastname: Proeschel
authors.forename: J
authors.initials: J
authors.lastname: Raum
mesh_terms: D000328:Adult; D001732:Bite Force; D004576:Electromyography / Q000295:instrumentation; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D005502:Food; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008280:Magnetics / Q000295:instrumentation; D008297:Male; D008406:Masseter Muscle / Q000502:physiology; D008409:Mastication / Q000502:physiology; D008410:Masticatory Muscles / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D009334:Neck Muscles / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013703:Temporal Muscle / Q000502:physiology; D014159:Transducers