title: Stride-to-stride variability is altered during backward walking in anterior cruciate ligament deficient patients.
abstract: BACKGROUND
  Recently backward walking is used by physical therapists to strengthen the hamstring muscles and thus improve the function of the knee joint of anterior cruciate ligament deficient patients. The aim of this study was to examine the stride-to-stride variability of anterior cruciate ligament deficient patients during backward walking. The variation of how a motor behavior emerges in time is best captured by tools derived from nonlinear dynamics, for which the temporal sequence in a series of values is the facet of interest.
  
  
  METHODS
  Fifteen patients with unilateral anterior cruciate ligament deficiency and eleven healthy controls walked backwards at their self-selected speed on a treadmill while three-dimensional knee kinematics were collected (100 Hz). A nonlinear measure, the largest Lyapunov Exponent was calculated from the resulted knee joint flexion-extension data of both groups to assess the stride-to-stride variability.
  
  
  RESULTS
  Both knees of the deficient patients exhibited significantly lower Lyapunov Exponent values as compared to the healthy control group revealing more rigid movement pattern. The intact knee of the deficient patients showed significantly lower Lyapunov Exponent values as compared to the deficient knee.
  
  
  CONCLUSIONS
  Anterior cruciate ligament (ACL) deficiency leads to loss of optimal variability regardless of the walking direction (forwards in previous studies or backwards here) as compared to healthy individuals. This could imply diminished functional responsiveness to the environmental demands for both knees of ACL deficient patients which could result in the knees being more susceptible to injury.
authors.affiliation: Orthopaedic Sports Medicine Center, Department of Orthopaedic Surgery, University of Ioannina, Ioannina, Greece.
authors.forename: Franceska
authors.initials: F
authors.lastname: Zampeli
authors.forename: Constantina O
authors.initials: CO
authors.lastname: Moraiti
authors.forename: Sofia
authors.initials: S
authors.lastname: Xergia
authors.forename: Vasilis A
authors.initials: VA
authors.lastname: Tsiaras
authors.forename: Nicholas
authors.initials: N
authors.lastname: Stergiou
authors.forename: Anastasios D
authors.initials: AD
authors.lastname: Georgoulis
mesh_terms: D000328:Adult; D000465:Algorithms; D016118:Anterior Cruciate Ligament / Q000503:physiopathology; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D005684:Gait / Q000502:physiology*; D006801:Humans; D007717:Knee; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D026741:Physical Therapy Modalities; D013997:Time Factors; D016138:Walking