title: Skeletal muscle stiffness in static and dynamic contractions.
abstract: Series elastic stiffness of rat gastrocnemius medialis muscle was determined by means of sinusoidal movements (180 Hz, 0.25% of muscle length) for various contraction conditions. The effects of muscle length, activation level, velocity, prestretch, and temperature on the force-stiffness relationship were investigated. All force-stiffness curves were transformed to a linear force-alpha curve (Ettema and Huijing, 1993; Morgan, 1977) to distinguish mathematically two series elastic components; a force dependent and force independent compliance. For all isometric conditions a typical force-stiffness curve was found, where stiffness increased with force, and this increase levelled off at higher forces. Stiffness in dynamic shortening and lengthening contractions is related to force in a completely different way than in isometric condition. An increase in temperature caused a decrease in muscle stiffness for a given force, and the effects of muscle length, activation level, and prestretch were small. It was concluded that the series elastic component of skeletal-muscle-tendon complex is probably located in more than two morphologically identifiable elements. Furthermore, we concluded that using a single series elastic element in muscle modelling is not appropriate to describe muscle behaviour under all conditions that occur during in vivo activation.
authors.affiliation: Department of Anatomical Sciences, University of Queensland, Australia.
authors.forename: G J
authors.initials: GJ
authors.lastname: Ettema
authors.forename: P A
authors.initials: PA
authors.lastname: Huijing
mesh_terms: D000465:Algorithms; D000818:Animals; D004548:Elasticity; D004558:Electric Stimulation; D005246:Feedback; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000294:innervation / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012815:Signal Processing, Computer-Assisted; D013314:Stress, Mechanical; D013696:Temperature; D013710:Tendons / Q000033:anatomy & histology / Q000502:physiology; D013997:Time Factors; D014732:Vibration