title: Modulation of the Fibularis Longus Hoffmann Reflex and Postural Instability Associated With Chronic Ankle Instability.
abstract: BACKGROUND
  Individuals with chronic ankle instability (CAI) present with decreased modulation of the Hoffmann reflex (H-reflex) from a simple to a more challenging task. The neural alteration is associated with impaired postural control, but the relationship has not been investigated in individuals with CAI.
  
  
  OBJECTIVE
  To determine differences in H-reflex modulation and postural control between individuals with or without CAI and to identify if they are correlated in individuals with CAI.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Laboratory.
  
  
  METHODS
  A total of 15 volunteers with CAI (9 males, 6 females; age = 22.6 ± 5.8 years, height = 174.7 ± 8.1 cm, mass = 74.9 ± 12.8 kg) and 15 healthy sex-matched volunteers serving as controls (9 males, 6 females; age = 23.8 ± 5.8 years, height = 171.9 ± 9.9 cm, mass = 68.9 ± 15.5 kg) participated.
  
  
  METHODS
  Maximum H-reflex (Hmax) and motor wave (Mmax) from the soleus and fibularis longus were recorded while participants lay prone and then stood in unipedal stance. We assessed postural tasks of unipedal stance with participants' eyes closed for 10 seconds using a forceplate.
  
  
  METHODS
  We normalized Hmaxto Mmaxto obtain Hmax: Mmaxratios for the 2 positions. For each muscle, H-reflex modulation was quantified using the percentage change scores in Hmax: Mmaxratios calculated from prone position to unipedal stance. Center-of-pressure data were used to compute 4 time-to-boundary variables. Separate independent-samples t tests were performed to determine group differences. Pearson product moment correlation coefficients were calculated between the modulation and balance measures in the CAI group.
  
  
  RESULTS
  The CAI group presented less H-reflex modulation in the soleus (t26= -3.77, P = .001) and fibularis longus (t25= -2.59, P = .02). The mean of the time-to-boundary minima in the anteroposterior direction was lower in the CAI group (t28= -2.06, P = .048). We observed a correlation (r = 0.578, P = .049) between the fibular longus modulation and mean of time-to-boundary minima in the anteroposterior direction.
  
  
  CONCLUSIONS
  The strong relationship indicated that, as H-reflex amplitude in unipedal stance was less down modulated, unipedal postural control was more impaired. Given the deficits in H-reflex modulation and postural control in the CAI group, the relationship may provide insights into the neurophysiologic mechanism of postural instability.
authors: Department of Kinesiology and Sport Sciences, University of Miami, FL.
authors: Kyung-Min
authors: KM
authors: Kim
authors: Department of Kinesiology, University of Virginia, Charlottesville.
authors: Joseph M
authors: JM
authors: Hart
authors: Department of Kinesiology, University of Virginia, Charlottesville.
authors: Susan A
authors: SA
authors: Saliba
authors: Department of Kinesiology, University of Virginia, Charlottesville.
authors: Jay
authors: J
authors: Hertel
mesh_terms: D000843:Ankle Joint / Q000503:physiopathology*; D002908:Chronic Disease; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007866:Leg / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D055815:Young Adult
keywords: ankle muscles; balance; postural-control deficits; soleus muscle; spinal mechanism