title: Contractile adaptations in the human triceps surae after isometric exercise.
abstract: Ultrastructural and twitch contractile characteristics of the human triceps surae were determined in seven healthy but very sedentary subjects before and after 16 wk of unilateral isometric training at 100% maximal voluntary contraction. After training, twitch contraction time decreased by approximately 20%. One-half relaxation time, peak twitch torque, and percent fiber type in any of the muscles of the triceps surae complex were not changed by training. Type I and type II fiber areas increased in the soleus by approximately 30%, but only type II fibers showed an increased in area in the lateral gastrocnemius (40%). Despite such changes in fiber area, the volume density of the sarcoplasmic reticulum-transverse tubular (SR) network averaged 3.2 +/- 0.6 and 5.9 +/- 0.9% in type I and type II fibers, respectively, before and after training in the two heads of the gastrocnemius. Type I SR fraction increased to 3.5 +/- 1.2% after training in the soleus; however, correlations were not significant between the change in the volume density of SR and the change in twitch contraction time (R = 0.46, P = 0.45) or the change in one-half relaxation time (R = -0.68, P = 0.08). The results demonstrate that isometric training at 100% maximal voluntary contraction induced changes in twitch contraction time that were not directly related to changes in the volume density of SR in fibers of the triceps surae.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: S E
authors.initials: SE
authors.lastname: Alway
authors.forename: J D
authors.initials: JD
authors.lastname: MacDougall
authors.forename: D G
authors.initials: DG
authors.lastname: Sale
mesh_terms: D000328:Adult; D001707:Biopsy, Needle; D004558:Electric Stimulation; D015444:Exercise; D006651:Histocytochemistry; D006801:Humans; D008297:Male; D008854:Microscopy, Electron; D009119:Muscle Contraction; D009132:Muscles / Q000032:analysis / Q000648:ultrastructure