title: Gender differences on ultrasound imaging of lateral abdominal muscle thickness in asymptomatic adults: a pilot study.
abstract: OBJECTIVE
  To describe gender and side-to-side differences in lateral abdominal wall muscle thickness at rest and during contraction in asymptomatic adults.
  
  
  METHODS
  Cross-sectional observational study.
  
  
  METHODS
  Tertiary university outpatient musculoskeletal clinic.
  
  
  METHODS
  Asymptomatic, healthy adults.
  
  
  METHODS
  A single examiner with training in ultrasound (US) assessment evaluated all subjects and used a different hand to guide the US transducer on each side. Bilateral anteroposterior measurements of transversus abdominis (TrA) and internal oblique (IO) thickness were assessed at rest and during maximal contraction with the use of an abdominal draw-in maneuver (ADM). Three sets of data points were obtained on 12 subjects to determine intrarater reliability within a single session.
  
  
  METHODS
  Anteroposterior thickness of TrA and IO muscles (cm).
  
  
  RESULTS
  A total of 20 subjects (mean age, 29.3 years; range, 23-46 years; 8 men and 12 women; mean body mass index, 24.4 kg/m(2); range, 18.9-34.9 kg/m(2)) were examined. At rest, men had greater TrA and IO thickness compared with women (men, 0.55, and women, 0.35, P = .01; and men, 0.95, and women, 0.77, P = .04, respectively). At rest, there were no side-to-side differences of TrA or IO muscles for both genders. With an ADM, women demonstrated a significant percent change in thickness of their TrA muscle compared with men (women, 0.77, and men, 0.29, P = .001). No significant difference was found between men and women in the percent change of IO thickness with ADM (women, 0.20, and men, 0.12, P = .24). There was excellent intrarater reliability for measurements of the right abdominal muscles (intraclass correlation coefficient = 0.92-0.95) and moderate-to-good intrarater reliability for measurements of the left abdominal muscles (intraclass correlation coefficient = 0.62-0.92).
  
  
  CONCLUSIONS
  Asymptomatic men have greater TrA and IO thickness at rest compared with asymptomatic women; however, women demonstrated a greater percent change in TrA thickness with an ADM compared with men.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Rehabilitation Institute of Chicago/Northwestern University Feinberg School of Medicine, 345 E. Superior St, Chicago, IL 60611, USA. mrho@ric.org
authors.forename: Monica
authors.initials: M
authors.lastname: Rho
authors.forename: Theresa
authors.initials: T
authors.lastname: Spitznagle
authors.forename: Linda
authors.initials: L
authors.lastname: Van Dillen
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Maheswari
authors.forename: Sonal
authors.initials: S
authors.lastname: Oza
authors.forename: Heidi
authors.initials: H
authors.lastname: Prather
mesh_terms: D000009:Abdominal Muscles / Q000000981:diagnostic imaging* / Q000502:physiology; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D010865:Pilot Projects; D012146:Rest; D012737:Sex Factors; D014463:Ultrasonography