title: Voluntary activation of trapezius measured with twitch interpolation.
abstract: This study investigated the feasibility of measuring voluntary activation of the trapezius muscle with twitch interpolation. Subjects (n=8) lifted the right shoulder or both shoulders against fixed force transducers. Stimulation of the accessory nerve in the neck was used to evoke maximal twitches in right trapezius. The twitch-like increments in force (superimposed twitches) evoked during different strength voluntary contractions were linearly related to voluntary force (r=-0.82 to -0.99). Hence, voluntary activation could be quantified by twitch interpolation with this stimulus. Comparison of unilateral and bilateral MVCs showed that maximal voluntary force was greater in unilateral than bilateral efforts (92.7+/-2.9% and 82.3+/-5.8% MVC, respectively) but voluntary activation was similar (88.6+/-9.6% and 91.7+/-5.2%). Trapezius is commonly affected in work-related musculoskeletal disorders. Measurement of voluntary activation will be a useful technique to demonstrate whether the reduced maximal voluntary force reported in such disorders is due to muscular or neural factors.
authors.affiliation: Prince of Wales Medical Research Institute, Barker Street, Randwick, Sydney, NSW 2031, Australia. jl.taylor@unsw.edu.au
authors.forename: Janet L
authors.initials: JL
authors.lastname: Taylor
authors.forename: Henrik Baare
authors.initials: HB
authors.lastname: Olsen
authors.forename: Gisela
authors.initials: G
authors.lastname: Sjøgaard
authors.forename: Karen
authors.initials: K
authors.lastname: Søgaard
mesh_terms: D000328:Adult; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology; D014836:Volition / Q000502:physiology*