title: Effects of repeated lengthening contractions on skeletal muscle adaptations in female rats.
abstract: We examined the adaptation of plantar flexor muscles of female rats to 6 weeks (5 days/week) of lengthening contractions. After repeated lengthening contractions, a decrease in myofiber area of gastrocnemius medialis (26%) was accompanied by an increase in extracellular matrix (ECM) (42%) and collagen content (30.9%) without changes in muscle mass. Decrease in myofiber area (13%) and muscle mass of soleus (19%) was associated with increased collagen content (28%) and ECM (15%). Relative number of soleus myofibers stained for fast myosin increased by 26%. For plantaris, increases in collagen content (32.3%), percent ECM (17%), and myofiber area (6%) were recorded. We also observed (1) increases (3.3%) in the collagen content of the Achilles tendon, (2) no change in the crosslink content of any of the tissues tested, and (3) no difference in the force-frequency relationship of the plantar flexor muscles. Substantial decreases in myofiber areas with increases in muscle connective tissue by 6 weeks of repeated lengthening contractions did not appear to result in isometric force loss.
authors.affiliation: Department of Physiology and Pharmacology, Robert C. Byrd Health Sciences Center, School of Medicine, West Virginia University, Morgantown, WV 26506-9229, USA. m.willems@chi.ac.uk
authors.forename: Mark E T
authors.initials: ME
authors.lastname: Willems
authors.forename: Gerald R
authors.initials: GR
authors.lastname: Miller
authors.forename: Francoise D
authors.initials: FD
authors.lastname: Stauber
authors.forename: William T
authors.initials: WT
authors.lastname: Stauber
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D005260:Female; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D009929:Organ Size / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley