title: Joint stabilizing response to expected and unexpected tilts.
abstract: BACKGROUND
  The results found in the literature regarding functional ankle joint stabilization are controversial possibly because of the testing methods used.
  
  
  METHODS
  The responses of 22 subjects to unexpected and expected sudden inversions of the foot were compared for all subjects together, as well as grouped by their self-perceived stability. A three-dimensional foot model was used to describe ankle and foot motion. Electromyographic signals of six muscles of the lower limb as well as the horizontal ground reaction forces were recorded.
  
  
  RESULTS
  Whereas unexpected and expected trials did not show significant differences (p > 0.05) in kinematics, higher activation and horizontal force integrals were found for the unexpected trials. In addition, no differences in electromyographic or ground reaction force parameters were found between stable and unstable ankles; however, the kinematics revealed higher amplitudes and velocities for the stable group.
  
  
  CONCLUSIONS
  The awareness of the instant of tilt enhances stabilization in that the same motion is achieved with a lower muscle activation. Evidence suggests that this is triggered at supraspinal levels. We found that timing of the EMG signal is not as relevant to stabilization as the amplitude (which has often been disregarded in the literature).
authors.affiliation: German Sport University Cologne, Institute for Biomechanics and Orthopaedics, Car-Diem-Weg 6, Cologne 50933, Germany. morey@dshs-koeln.de
authors.forename: Gaspar
authors.initials: G
authors.lastname: Morey-Klapsing
authors.forename: Adamantios
authors.initials: A
authors.lastname: Arampatzis
authors.forename: Gert-Peter
authors.initials: GP
authors.lastname: Brueggeman
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D005528:Foot / Q000502:physiology*; D006801:Humans; D008297:Male; D010465:Perception