title: Vastus lateralis fascicle length changes during stair ascent and descent.
abstract: METHODS
  Experimental descriptive laboratory study.
  
  
  OBJECTIVE
  To describe the change in fascicle length of the human vastus lateralis (VL) muscle during the stance phase of stair ascent and descent.
  
  
  BACKGROUND
  Muscle fascicle length changes during lower limb functional activities, such as walking and jumping, do not always coincide with joint angle changes.
  
  
  METHODS
  Thirty-three healthy, college-age women walked up and down 4 standard steps. VL fascicle length and pennation angle were measured using real-time ultrasonography. Knee angle was monitored using an electrical goniometer. Foot switches indicated foot contact and release. VL muscle activity was monitored using surface electrodes. The VL muscle-tendon complex and tendon length were calculated based on published models.
  
  
  RESULTS
  During initial weight acceptance in stair ascent, the knee joint extended only 3 degrees , VL muscle activity increased to a maximum, VL fascicles shortened, and the tendon lengthened. As the knee extended to ascend the step, the fascicles and tendon shortened throughout the movement. During weight acceptance in stair descent, VL muscle activity increased, VL fascicle length did not change significantly, but the tendon lengthened as 10 degrees of knee flexion occurred. As the knee flexed to complete descent, VL muscle activity peaked, and VL fascicles and tendon lengthened.
  
  
  CONCLUSIONS
  VL fascicles shorten and lengthen as expected during the respective knee extension and knee flexion phases of stair ascent and descent. However, during initial weight acceptance in both stair ascent and descent, the fascicle length change did not coincide with the knee joint kinematics.
authors.affiliation: School of Physical Therapy and the Interdisciplinary Institute for Neuromusculoskeletal Research, Ohio University, Athens, OH 45701, USA. chleboun@ohio.edu
authors.forename: Gary S
authors.initials: GS
authors.lastname: Chleboun
authors.forename: Sarah T
authors.initials: ST
authors.lastname: Harrigal
authors.forename: James Z
authors.initials: JZ
authors.lastname: Odenthal
authors.forename: Laura A
authors.initials: LA
authors.lastname: Shula-Blanchard
authors.forename: Jennifer N
authors.initials: JN
authors.lastname: Steed
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology; D013710:Tendons / Q000000981:diagnostic imaging / Q000502:physiology; D014463:Ultrasonography