title: Effect of muscle length on voluntary activation of the plantar flexors in boys and men.
abstract: OBJECTIVE
  The aim of the present study was to compare the effect of muscle length on the maximal voluntary activation level (VA) of the plantar-flexors between children and adults.
  
  
  METHODS
  Fourteen boys (10.0 ± 1.0 years) and fifteen men (24.6 ± 4.2 years) performed 5-s maximal isometric voluntary contractions (MVC) of the plantar-flexor muscles at seven ankle angles [from 10° in dorsi-flexion (DF) to 20° in plantar-flexion (PF); 0° = reference position; the angle between the plantar surface and leg is a right angle]. Single magnetic stimulations were delivered to the posterior tibial nerve during MVCs to determine VA.
  
  
  RESULTS
  Results showed a higher absolute torque of the plantar-flexor muscles at long (10° DF) than at short muscle length (20° PF) in men (89.4 ± 19.4 vs. 46.8 ± 17.0 N m, P < 0.001) and boys (44.9 ± 18.5 vs. 26.6 ± 12.8 N m, P < 0.001). On average, VA was significantly higher in men than in boys (92.4 ± 1.7 vs. 87.6 ± 1.6 %, P < 0.05). However, no significant main effect of the ankle angle was observed on VA.
  
  
  CONCLUSIONS
  The VA partly accounts for the plantar-flexors MVC torque difference between children and adults but is not affected by the muscle length changes in both groups. Therefore, VA cannot account for the shape of the torque-angle relationship on the plantar-flexor muscles.
authors.affiliation: Clermont Auvergne University, Blaise Pascal University, EA 3533, Laboratory of Metabolic Adaptations During Exercise in Physiological and Pathological Conditions (AME2P), BP 80026, F-63171, Aubière Cedex, France.|Decathlon Research, Department of Movement Sciences, Villeneuve d'Asq, France.
authors.forename: Virginie
authors.initials: V
authors.lastname: Kluka
authors.affiliation: Clermont Auvergne University, Blaise Pascal University, EA 3533, Laboratory of Metabolic Adaptations During Exercise in Physiological and Pathological Conditions (AME2P), BP 80026, F-63171, Aubière Cedex, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Martin
authors.affiliation: Clermont Auvergne University, Blaise Pascal University, EA 3533, Laboratory of Metabolic Adaptations During Exercise in Physiological and Pathological Conditions (AME2P), BP 80026, F-63171, Aubière Cedex, France.
authors.forename: Sebastian Garcia
authors.initials: SG
authors.lastname: Vicencio
authors.affiliation: Clermont University Hospital, Clermont-Ferrand, France.
authors.forename: Mathias
authors.initials: M
authors.lastname: Giustiniani
authors.affiliation: Clermont University Hospital, Clermont-Ferrand, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Morel
authors.affiliation: Decathlon Research, Department of Movement Sciences, Villeneuve d'Asq, France.
authors.forename: Cédric
authors.initials: C
authors.lastname: Morio
authors.affiliation: Clermont University Hospital, Clermont-Ferrand, France.|INRA, Unité de Nutrition Humaine (UNH, UMR 1019), CRNH Auvergne, Clermont-Ferrand, France.|Université Clermont Auvergne, Université d'Auvergne, Clermont-Ferrand, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Coudeyre
authors.affiliation: Clermont Auvergne University, Blaise Pascal University, EA 3533, Laboratory of Metabolic Adaptations During Exercise in Physiological and Pathological Conditions (AME2P), BP 80026, F-63171, Aubière Cedex, France. sebastien.ratel@univ-bpclermont.fr.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Ratel
mesh_terms: D000328:Adult; D000842:Ankle / Q000502:physiology; D000843:Ankle Joint / Q000502:physiology; D002648:Child; D004576:Electromyography / Q000379:methods; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007866:Leg / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque; D055815:Young Adult
keywords: Childhood; Magnetic stimulation; Motor unit recruitment; Torque