title: Effects of short length immobilization of medial gastrocnemius muscle of growing young adult rats.
abstract: Effects of four and six weeks of immobilization at short length of gastrocnemius muscle on its architecture at optimum muscle length and length-force characteristics were studied. In general, immobilization effects were similar after 4 and 6 weeks. Smaller physiological cross-sectional area and lower muscle force were found as a consequence of immobilization. Muscle and aponeurosis were shorter. This was shown to be quantitatively related to atrophy i.e. smaller fibre diameter. Despite this atrophy no effects of immobilization on fibre and aponeurosis angles could be shown. Adaptation of the number of sarcomeres in series was found exclusively in distal fibres after 4 weeks of immobilization. No significant effects were found for proximal fibres of muscles at this time nor for any fibres after 6 weeks of immobilization. The effects of immobilization on muscle architecture did not affect the length range of active force exertion. It is concluded that muscle length adaptation as a consequence of short length immobilization is not related to adaptation of number of sarcomeres in series but to the occurrence of atrophy. It is also concluded that atrophy of pennate muscles does not have to be accompanied by a lower fibre and aponeurosis angle. Comparison of immobilized and control group rats indicates that the effects of immobilization can be characterized as a combination of retarded development of several variables and the influence of atrophy and its consequences.
authors.affiliation: Vakgroep Functionele Anatomie, Faculteit Bewegingswetenschappen, Vrije Universiteit Amsterdam, The Netherlands.
authors.forename: J W
authors.initials: JW
authors.lastname: Heslinga
authors.forename: P A
authors.initials: PA
authors.lastname: Huijing
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D007103:Immobilization / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D024510:Muscle Development; D009132:Muscles / Q000033:anatomy & histology*; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000502:physiology*