130 ORIGINAL RESEARCH REPORT Journal of Sport Rehabilitation, 2015, 24, 130 -139 http://dx.doi.org/10.1123/jsr.2013-0123 © 2015 Human Kinetics, Inc. Kim is with the Dept of Health and Human Performance, Texas State University, San Marcos, TX. Ingersoll is with the College of Health Sciences, University of Toledo, Toledo, OH. Hertel is with the Dept of Kinesiology, University of Virginia, Char- lottesville, VA. Address author correspondence to Kyung-Min Kim at kmk102@txstate.edu. Chronic ankle instability (CAI) is a somewhat common consequence of an ankle sprain. 1 It is estimated that approximately 30% of patients suffering initial ankle sprains develop CAI. 2 CAI is primarily characterized by repetitive bouts of the ankle giving way, the feeling of ankle-joint instability, and self-reported ankle disability that present for a minimum of 1 year after the initial sprain. 3 Individuals with CAI have also been reported to have an increased incidence of recurrent ankle injuries and a lower health-related quality of life. 3,4 Furthermore, an increased likelihood to develop ankle osteoarthritis has been reported in patients with repetitive ankle sprains. 5 Although a variety of predisposing factors have been proposed in the literature to better understand CAI, the mechanism responsible for the development of CAI remains unclear. Arthrogenic muscle inhibition (AMI) has been proposed as one of the underlying neurophysiological mechanisms responsible for the sensorimotor deicits associated with CAI. 6–8 AMI has been deined as an on-going relexive inhibition of the undamaged muscles surrounding a joint after distension or damage to the ligamentous structures of that joint. 9 Recent systematic reviews concluded that neural alteration exists in patients with a history of knee injuries or knee osteoarthritis, as evidenced by volitional activation failure of the quadriceps. 10,11 The diminished ability to adequately recruit motoneurons to the quadriceps is thought to be an underlying mechanism of sensorimotor dysfunction that may contribute to early onset of posttraumatic knee osteoarthritis. 12 In addition to the quadriceps AMI in patients with knee pathology, recent studies 6–8 have been conducted to determine if AMI was present in patients with CAI. The studies used Hoffmann relex (H-relex) to determine presence of AMI in the muscles of interest. H-relex is a spinal relex similar to the stretch relex, Facilitation of Hoffmann Reflexes of Ankle Muscles in Prone but Not Standing Positions by Focal Ankle-Joint Cooling Kyung-Min Kim, Christopher D. Ingersoll, and Jay Hertel Context: Focal ankle-joint cooling (FAJC) has been shown to increase Hoffmann (H) relex amplitudes of select leg muscles while subjects lie prone, but it is unknown whether the neurophysiological cooling effects persist in standing. Objective: To assess the effects of FAJC on H-relexes of the soleus and ibularis longus during 3 body positions (prone, bipedal, and unipedal stances) in individuals with and without chronic ankle instability (CAI). Design: Crossover. Setting: Laboratory. Participants: 15 young adults with CAI (9 male, 6 female) and 15 healthy controls. Intervention: All subjects received both FAJC and sham treatments on separate days in a randomized order. FAJC was accomplished by applying a 1.5-L plastic bag illed with crushed ice to the ankle for 20 min. Sham treatment involved room-temperature candy corn. Main Outcome Measures: Maximum amplitudes of H-relexes and motor (M) waves were recorded while subjects lay prone and then stood in quiet bipedal and unipedal stances before and immediately after each treatment. Primary outcome measures were H max :M max ratios for the soleus and ibularis longus. Three-factor (group × treatment condition × time) repeated-measures ANOVAs and Fisher LSD tests were performed for statistical analyses. Results: Signiicant interactions of treatment condition by time for prone H max :M max ratios were found in the soleus (P = .001) and ibularis longus (P = .003). In both muscles, prone H max :M max ratios moderately increased after FAJC but not after sham treatment. The CAI and healthy groups responded similarly to FAJC. In contrast, there were no signiicant interactions or main effects in the bipedal and unipedal stances in either muscle (P > .05). Conclusions: FAJC moderately increased H-relex amplitudes of the soleus and ibularis longus while subjects were prone but not during bipedal or unipedal standing. These results were not different between groups with and without CAI. Keywords: arthrogenic muscle inhibition, disinhibitory modality, chronic ankle instability, cryotherapy