title: Twitch contractile adaptations are not dependent on the intensity of isometric exercise in the human triceps surae.
abstract: Ultrastructural and twitch contractile characteristics of the human triceps surae were determined in six healthy but very sedentary subjects before and after 16 weeks of isometric training at 30% maximal voluntary contraction (MVC). Following training, twitch contraction time was approximately 16% shorter, although no differences were observed in one-half relaxation time or peak twitch torque. Percent fibre type was not changed by training. The mean area of type I and type II fibres in the soleus increased by approximately 30% but only type II fibres showed an increase in area in the lateral gastrocnemius (30%). Despite such changes in fibre area the volume density of the sarcoplasmic reticulum-transverse tubular network averaged 3.2 +/- 0.6% and 5.9 +/- 0.9% in type I and type II fibres respectively, before and after training in the two heads of the gastrocnemius. The results indicate that contractile adaptations to isometric training at 30% MVC were limited to twitch contraction time and were not directly related to changes in percent fibre distribution or the volume of sarcoplasmic reticulum and transverse tubules in either type I or type II fibres. The data further demonstrate that substantial fibre hypertrophy is achieved by training with low-intensity contractions.
authors.affiliation: School of Health, Physical Education and Recreation, Ohio State University, Columbus 43210-1284.
authors.forename: S E
authors.initials: SE
authors.lastname: Alway
authors.forename: D G
authors.initials: DG
authors.lastname: Sale
authors.forename: J D
authors.initials: JD
authors.lastname: MacDougall
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D015444:Exercise; D006801:Humans; D007866:Leg; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000033:anatomy & histology / Q000502:physiology* / Q000648:ultrastructure; D010806:Physical Education and Training