title: The effect of angular velocity and cycle on the dissipative properties of the knee during passive cyclic stretching: a matter of viscosity or solid friction.
abstract: BACKGROUND
  The mechanisms behind changes in mechanical parameters following stretching are not understood clearly. This study assessed the effects of joint angular velocity on the immediate changes in passive musculo-articular properties induced by cyclic stretching allowing an appreciation of viscosity and friction, and their contribution to changes in torque that occur.
  
  
  METHODS
  Ten healthy subjects performed five passive knee extension/flexion cycles on a Biodex dynamometer at five preset angular velocities (5-120 deg/s). The passive torque and knee angle were measured, and the potential elastic energy stored during the loading and the dissipation coefficient were calculated.
  
  
  RESULTS
  As the stretching velocity increased, so did stored elastic energy and the dissipation coefficient. The slope of the linear relationship between the dissipation coefficient and the angular velocity was unchanged across repetitions indicating that viscosity was unlikely to be affected. A difference in the y-intercept across repetitions 1 and 5 was indicative of a change in processes associated with solid friction. Electromyographical responses to stretching were low across all joint angular velocities.
  
  
  CONCLUSIONS
  Torque changes during cyclic motion may primarily involve solid friction which is more indicative of rearrangement/slipping of collagen fibers rather than the redistribution of fluid and its constituents within the muscle. The findings also suggest that it is better to stretch slowly initially to reduce the amount of energy absorption required by tissues, but thereafter higher stretching speeds can be undertaken.
authors.affiliation: Université de Nantes, Nantes Atlantique Universités, Laboratoire Motricité, Interactions, Performance, EA 4334, UFR STAPS, 25 bis Bd Guy Mollet BP 72206, Nantes F-44000, France. antoine.nordez@univ-nantes.fr
authors.forename: A
authors.initials: A
authors.lastname: Nordez
authors.forename: P J
authors.initials: PJ
authors.lastname: McNair
authors.forename: P
authors.initials: P
authors.lastname: Casari
authors.forename: C
authors.initials: C
authors.lastname: Cornu
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D004548:Elasticity / Q000502:physiology; D004576:Electromyography; D004735:Energy Transfer / Q000502:physiology*; D017276:Friction; D006358:Hot Temperature; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007717:Knee / Q000502:physiology; D007719:Knee Joint / Q000737:chemistry / Q000502:physiology*; D008297:Male; D053581:Muscle Strength Dynamometer; D052580:Muscle Stretching Exercises; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013848:Thigh; D019415:Torque; D014783:Viscosity