title: The medial gastrocnemius muscle attenuates force fluctuations during plantar flexion.
abstract: Force fluctuations during steady contractions of multiple agonist muscles may be influenced by the relative contribution of force by each muscle. The purpose of the study was to compare force fluctuations during steady contractions performed with the plantar flexor muscles in different knee positions. Nine men (25.8+/-5.1 years) performed steady contractions of the plantar flexor muscles in the knee-flexed and knee-extended (greater involvement of the gastrocnemii muscles) positions. The maximal voluntary contraction (MVC) force was 32% greater in the knee-extended position compared with the knee-flexed position. The target forces were 2.5-10% MVC force in the respective position. The amplitude of electromyogram in the medial gastrocnemius muscle was greater in the knee-extended position (10.50+/-9.80%) compared with the knee-flexed position (1.26+/-1.15%, P<0.01). The amplitude of electromyogram in the soleus muscle was not influenced by the knee position. The amplitude of electromyogram in the lateral gastrocnemius and tibialis anterior muscles was marginal and unaltered with knee position. At the same force (in Newtons), the standard deviation of force was lower in the knee-extended position compared with the knee-flexed position. These results indicate that force fluctuations during plantar flexion are attenuated with greater involvement of the medial gastrocnemius muscle.
authors.affiliation: Department of Integrative Physiology, University of Colorado, Clare Room 114, 354 UCB, Boulder, 80309-0354, USA. shinohara@colorado.edu
authors.forename: Minoru
authors.initials: M
authors.lastname: Shinohara
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Yoshitake
authors.forename: Motoki
authors.initials: M
authors.lastname: Kouzaki
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukunaga
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004576:Electromyography / Q000379:methods; D006801:Humans; D007719:Knee Joint / Q000294:innervation / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D013057:Spectrum Analysis