title: Differences in lateral drop jumps from an unknown height among individuals with functional ankle instability.
abstract: BACKGROUND
  Functional ankle instability (FAI) is a debilitating condition that has been reported to occur after 20% to 50% of all ankle sprains. Landing from a jump is one common mechanism of ankle injury, yet few researchers have explored the role of visual cues and anticipatory muscle contractions, which may influence ankle stability, in lateral jumping maneuvers.
  
  
  OBJECTIVE
  To examine muscle-activation strategies between FAI and stable ankles under a lateral load and to evaluate the differences in muscle activation in participants with FAI and participants with stable ankles when they were unable to anticipate the onset of lateral loads during eyes-open versus eyes-closed conditions.
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  Controlled laboratory setting.
  
  
  METHODS
  A total of 40 people participated: 20 with FAI and 20 healthy, uninjured, sex- and age-matched persons (control group).
  
  
  METHODS
  Participants performed a 2-legged lateral jump off a platform onto a force plate set to heights of 35 cm or 50 cm and then immediately jumped for maximal height. They performed jumps in 2 conditions (eyes open, eyes closed) and were unaware of the jump height when their eyes were closed.
  
  
  METHODS
  Amplitude normalized electromyographic (EMG) area (%), peak (%), and time to peak in the tibialis anterior (TA), peroneus longus (PL), and lateral gastrocnemius (LG) muscles were measured.
  
  
  RESULTS
  Regardless of the eyes-open or eyes-closed condition, participants with FAI had less preparatory TA (t158 = 2.22, P = .03) and PL (t158 = 2.09, P = .04) EMG area and TA (t158 = 2.45, P = .02) and PL (t158 = 2.17, P = .03) peak EMG than control-group participants.
  
  
  CONCLUSIONS
  By removing visual cues, unanticipated lateral joint loads occurred simultaneously with decreased muscle activity, which may reduce dynamic restraint capabilities in persons with FAI. Regardless of visual impairment and jump height, participants with FAI exhibited PL and TA inhibition, which may limit talonavicular stability and intensify lateral joint surface compression and pain.
authors: Department of Kinesiology, University of Georgia, Athens.
authors: Adam
authors: A
authors: Rosen
authors: Charles
authors: C
authors: Swanik
authors: Stephen
authors: S
authors: Thomas
authors: Joseph
authors: J
authors: Glutting
authors: Christopher
authors: C
authors: Knight
authors: Thomas W
authors: TW
authors: Kaminski
mesh_terms: D000842:Ankle / Q000502:physiology / Q000503:physiopathology; D016512:Ankle Injuries / Q000503:physiopathology*; D000843:Ankle Joint / Q000502:physiology* / Q000503:physiopathology; D016022:Case-Control Studies; D003463:Cues; D004576:Electromyography; D056228:Feedback, Sensory; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology*; D033081:Shear Strength / Q000502:physiology; D013180:Sprains and Strains / Q000503:physiopathology; D013639:Tarsal Bones / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology
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