title: Active stiffness and strength in people with unilateral anterior shoulder instability: a bilateral comparison.
abstract: BACKGROUND
  Active muscle stiffness might protect the unstable shoulder from recurrent dislocation.
  
  
  OBJECTIVE
  To compare strength and active stiffness in participants with unilateral anterior shoulder instability and to examine the relationship between active stiffness and functional ability.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Participants included 16 males (age range, 16-40 years; height = 179.4 ± 6.1 cm; mass = 79.1 ± 6.8 kg) with 2 or more episodes of unilateral traumatic anterior shoulder instability.
  
  
  METHODS
  Active stiffness and maximal voluntary strength were measured bilaterally in participants. In addition, quality of life, function, and perceived instability were measured using the Western Ontario Stability Index, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, and Single Alpha Numeric Evaluation, respectively.
  
  
  RESULTS
  We found less horizontal adduction strength (t(15) = -4.092, P = .001) and less stiffness at 30% (t(14) = -3.796, P = .002) and 50% (t(12) = -2.341, P = .04) maximal voluntary strength in the unstable than stable shoulder. Active stiffness was not correlated with quality of life, function, or perceived instability (r range, 0.0-0.25; P > .05).
  
  
  CONCLUSIONS
  The observed reduction in stiffness in the unstable shoulder warrants inclusion of exercises in the rehabilitation program to protect the joint from perturbations that might lead to dislocation. The lack of association between active stiffness and quality of life, function, or perceived instability might indicate that stiffness plays a less direct role in shoulder stability.
authors.affiliation: Health and Rehabilitation Research Centre, Auckland University of Technology, New Zealand. margie.olds@aut.ac.nz
authors.forename: Margie
authors.initials: M
authors.lastname: Olds
authors.forename: Peter
authors.initials: P
authors.lastname: McNair
authors.forename: Antoine
authors.initials: A
authors.lastname: Nordez
authors.forename: Christophe
authors.initials: C
authors.lastname: Cornu
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008297:Male; D009127:Muscle Rigidity / Q000503:physiopathology*; D053580:Muscle Strength / Q000502:physiology; D055502:Secondary Prevention; D012783:Shoulder Dislocation / Q000517:prevention & control; D012785:Shoulder Joint / Q000503:physiopathology*