title: Viscoelastic properties and flexibility of the human muscle-tendon unit in benign joint hypermobility syndrome.
abstract: OBJECTIVE
  To examine the passive energy absorption of the hamstring muscle-tendon unit in 9 women with benign joint hypermobility syndrome (BJHS) and 9 age and sex matched controls.
  
  
  METHODS
  Resistance to stretch was measured as knee flexion moment (N.m) with an isokinetic dynamometer during passive knee extension. The angle that induced a stretch sensation without pain was the maximal stretch angle. Force, angle, angular velocity (0.09 rad/s), and electromyograph were simultaneously and continuously recorded during the stretch. Hamstring cross sectional area was obtained with magnetic resonance imaging.
  
  
  RESULTS
  Forearm skin extensibility was greater for BJHS (3.6+/-0.5 cm) than for controls (1.3+/-0.2 cm) (p < 0.01). Similarly, the Beighton score was greater for BJHS (6.6+/-0.8) than for controls (0.4+/-0.2) (p < 0.001). Maximal stretch angle was greater for BJHS (delta1.35+/-0.07 rad) compared to controls (delta0.98+/-0.05 rad) (p < 0.001), and the corresponding peak moment was also greater for BJHS (1.3+/-0.4 Nm/cm2) than for controls (0.6+/-0.1 Nm/cm2) (p < 0.01). For a given mutual angle the passive energy absorption was the same for both groups, but at the maximal stretch angle the total area-normalized energy was greater for BJHS (0.36+/-0.04 J/cm2) than for controls (0.18+/-0.28 J/cm2) (p < 0.001).
  
  
  CONCLUSIONS
  The lack of difference in passive energy absorption for a given mutual stretch angle suggests that passive properties of the muscle-tendon unit of BJHS are similar to those of controls. However, the greater maximal stretch angle and corresponding peak moment in BJHS suggests a greater subjective tolerance to passive stretch. That is, increased flexibility in BJHS is not a function of altered passive properties of the muscle-tendon complex. It remains unknown if the enhanced tolerance to passive tension plays a role in the development of musculoskeletal ailment.
authors.affiliation: Team Danmark Test Center/Sports Medicine Research Unit, Clinical Unit of Preventive Medicine, and Department of Rheumatology, Bispebjerg Hospital, Copenhagen, Denmark. P.Magnusson@mfi.ku.dk
authors.forename: S P
authors.initials: SP
authors.lastname: Magnusson
authors.forename: C
authors.initials: C
authors.lastname: Julsgaard
authors.forename: P
authors.initials: P
authors.lastname: Aagaard
authors.forename: C
authors.initials: C
authors.lastname: Zacharie
authors.forename: S
authors.initials: S
authors.lastname: Ullman
authors.forename: T
authors.initials: T
authors.lastname: Kobayasi
authors.forename: M
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology; D007593:Joint Instability / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D018583:Pliability; D013577:Syndrome; D013710:Tendons / Q000503:physiopathology*; D016474:Weight-Bearing