title: Influence of vertical posture development on the velocity properties of triceps surae muscle in normal children.
abstract: Contraction time and half-relaxation time of triceps surae muscle were studied in 9 normal children immediately after they began to stand alone and again 6 weeks later. The velocity properties of the muscle were recorded during isometric twitch induced by supramaximal indirect stimulation. The development of the vertical posture at the end of the first year was found to be associated with prolongation of the contraction time, reaching values observed in 3-year-old children and adults. During the same period the half-relaxation time did not change. Data are reported to show that the influence of the vertical posture on the contraction time is due to changes in the contractile properties of the muscle. It is assumed that the velocity properties of triceps surae are influenced by the long-term activation of the muscle in supporting the vertical posture.
mesh_terms: D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007866:Leg; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D011187:Posture; D013997:Time Factors