title: Chronic Ankle Instability and Neural Excitability of the Lower Extremity.
abstract: BACKGROUND
  Neuromuscular dysfunction of the leg and thigh musculature, including decreased strength and postural control, is common in patients with chronic ankle instability (CAI). Understanding how CAI affects specific neural pathways may provide valuable information for targeted therapies.
  
  
  OBJECTIVE
  To investigate differences in spinal reflexive and corticospinal excitability of the fibularis longus and vastus medialis between limbs in patients with unilateral CAI and between CAI patients and participants serving as healthy controls.
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  Research laboratory.
  
  
  METHODS
  A total of 56 participants volunteered, and complete data for 21 CAI patients (9 men, 12 women; age = 20.81 ± 1.63 years, height = 171.57 ± 11.44 cm, mass = 68.84 ± 11.93 kg) and 24 healthy participants serving as controls (7 men, 17 women; age = 22.54 ± 2.92 years, height = 172.35 ± 10.85 cm, mass = 69.15 ± 12.30 kg) were included in the final analyses. Control participants were matched to CAI patients on sex, age, and limb dominance. We assigned "involved" limbs, which corresponded with the involved limbs of the CAI patients, to control participants.
  
  
  METHODS
  Spinal reflexive excitability was assessed via the Hoffmann reflex and normalized to a maximal muscle response. Corticospinal excitability was assessed using transcranial magnetic stimulation. Active motor threshold (AMT) was defined as the lowest transcranial magnetic stimulation intensity required to elicit motor-evoked potentials equal to or greater than 100 μV in 5 of 10 consecutive stimuli. We obtained motor-evoked potentials (MEPs) at percentages ranging from 100% to 140% of AMT.
  
  
  RESULTS
  Fibularis longus MEP amplitudes were greater in control participants than in CAI patients bilaterally at 100% AMT (control involved limb: 0.023 ± 0.031; CAI involved limb: 0.014 ± 0.008; control uninvolved limb: 0.021 ± 0.022; CAI uninvolved limb: 0.015 ± 0.007; F1,41 = 4.551, P = .04) and 105% AMT (control involved limb: 0.029 ± 0.026; CAI involved limb: 0.021 ± 0.009; control uninvolved limb: 0.034 ± 0.037; CAI uninvolved limb: 0.023 ± 0.013; F1,35 = 4.782, P = .04). We observed no differences in fibularis longus MEP amplitudes greater than 110% AMT and no differences in vastus medialis corticospinal excitability (P > .05). We noted no differences in the Hoffmann reflex between groups for the vastus medialis (F1,37 = 0.103, P = .75) or the fibularis longus (F1,41 = 1.139, P = .29).
  
  
  CONCLUSIONS
  Fibularis longus corticospinal excitability was greater in control participants than in CAI patients.
authors.affiliation: Department of Kinesiology, University of Toledo, OH;
authors.forename: Michelle M
authors.initials: MM
authors.lastname: McLeod
authors.affiliation: Department of Rehabilitation Sciences, University of Kentucky, Lexington;
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Gribble
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill. Dr McLeod is now with the Department of Health and Human Performance, College of Charleston, SC.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Pietrosimone
mesh_terms: D016512:Ankle Injuries / Q000503:physiopathology; D000843:Ankle Joint / Q000503:physiopathology*; D016022:Case-Control Studies; D002908:Chronic Disease; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D035002:Lower Extremity / Q000294:innervation / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology; D012018:Reflex / Q000502:physiology; D013127:Spinal Nerves / Q000502:physiology; D013848:Thigh / Q000503:physiopathology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Hoffmann reflex; lateral ankle sprain; transcranial magnetic stimulation