title: Duration of fascicle shortening is affected by muscle architecture and sex.
abstract: OBJECTIVE
  The purpose of this study was to examine muscle fascicle properties of the gastrocnemius medialis (GM) during contraction and stretch between males and females. During contraction muscle fascicles shorten and pennation angles increase to generate force. Due to the elastic nature of the attached tendon, the fascicles continue to shorten when maximal force is achieved in order to sustain isometric force and this duration of fascicle shortening (DFS) can be observed with ultrasonography. Linear and curved muscle fascicles both display these kinetics; however, it is currently unknown if static stretch prior to a maximal voluntary contraction (MVC) alters the DFS and whether the effect differs between males and females.
  
  
  METHODS
  Subjects performed an isometric MVC of the plantar flexors before and after a 2-min maximal dorsi-flexion stretch. Plantar flexor force was measured and ultrasound videography used to record GM and Achilles tendon architecture.
  
  
  RESULTS
  Males were stronger than females (p = 0.004). The DFS was longer for females compared to males (p = 0.001) and the addition of a static stretch increased the DFS for curved (p = 0.002), but not linear, fascicles. Curved fascicles were longer (p = 0.05) with larger pennation angles (p = 0.04) for both males and females when compared to linear fascicles. Tendon excursion was greater (p = 0.05) post-stretch during contraction when compared to pre-stretch.
  
  
  CONCLUSIONS
  This study provides evidence that regardless of sex, curved muscle fascicles behave differently than linear fascicles and should be considered separately when muscle architecture is examined.
authors.affiliation: School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada.
authors.forename: C L
authors.initials: CL
authors.lastname: Simpson
authors.affiliation: School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Arefin
authors.affiliation: School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada.
authors.forename: R R
authors.initials: RR
authors.lastname: Smart
authors.affiliation: School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada.
authors.forename: B
authors.initials: B
authors.lastname: Harwood
authors.affiliation: School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada. jennifer.jakobi@ubc.ca.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Jakobi
mesh_terms: D055119:Elastic Modulus / Q000502:physiology; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D010807:Physical Endurance / Q000502:physiology; D012737:Sex Factors; D013314:Stress, Mechanical; D013710:Tendons / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D013997:Time Factors; D014463:Ultrasonography; D055815:Young Adult
keywords: Fascicle curvature; Pennation angle; Stretching; Tendon; Ultrasound