title: The effects of agonist and antagonist muscle activation on the knee extension moment-angle relationship in adults and children.
abstract: The present study examined the effect of agonist activation and antagonist co-activation on the shape of the knee extension moment-angle relationship in adults and children. Isometric knee extension maximum voluntary contractions (MVCs) were performed at every 5 degrees of knee flexion between 55 degrees and 90 degrees (full extension = 0 degrees) by ten men, ten women, ten boys and ten girls. For each trial, the knee extensors' voluntary activation level was quantified using magnetic stimulation and the level of antagonist co-activation was quantified from their electromyographical activity. Peak MVC moment was greater for men (264 +/- 63 N m) than women (177 +/- 60 N m), and greater for adults than children (boys 78 +/- 17 N m, girls 91 +/- 28 N m) (p < 0.01). The agonistic activation level was greater for adults (approximately 85%) than children (approximately 70%). Similarly, antagonist co-activation was greater for adults than children, but relative to the agonist moment there were no differences between groups (all groups 7-8%). Correcting the peak moment for agonist and antagonist activation levels resulted in moments produced by fully activated agonist muscles of 334 +/- 83, 229 +/- 70, 114.2 +/- 32 and 147 +/- 46 N m, for men, women, boys and girls, respectively. Although correcting for shifts in joint angle during contraction altered the angle of peak moment by approximately 10 degrees (p < 0.01), the peak moment occurred at approximately 60 degrees for all groups. Changes in tendon stiffness, muscle size and architecture, and the pattern of the moment arm-angle relationship may in combination occur so that as children develop and mature into adults the shape of the moment-angle relationship is not altered.
authors.affiliation: Institute for Biomedical Research into Human Movement and Health (IRM), Manchester Metropolitan University, John Dalton Tower, Chester Street, Manchester, M1 5GD, UK. T.Obrien@hull.ac.uk
authors.forename: Thomas D
authors.initials: TD
authors.lastname: O'Brien
authors.forename: Neil D
authors.initials: ND
authors.lastname: Reeves
authors.forename: Vasilios
authors.initials: V
authors.lastname: Baltzopoulos
authors.forename: David A
authors.initials: DA
authors.lastname: Jones
authors.forename: Constantinos N
authors.initials: CN
authors.lastname: Maganaris
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology*; D002648:Child; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D019415:Torque