RESEARCH REPORT PLATFORM PRESENTATION

EFFECT OF LOCAL COOLING ON THE CORTICO-MOTOR EXCITABILITY OF ANKLE MUSCLES. Tremblay F¹, Dubé J, Adam P, Poirier M, Marcoux J; ¹Physiotherapy Program, School of Rehabilitation Sciences, University of Ottawa

PURPOSE: To determine the effect of local cooling on the corticomotor excitability of ankle muscles by means of transcranial magnetic stimulation (TMS). RELEVANCE: Local cooling is commonly used by physiotherapists as a hands-on modality to treat acute tissue injuries in the context of competitive sports or recreational activities. While the local effects of cooling are relatively well known, its influence at the central level are less known. PARTICIPANTS: Twelve young healthy adults (20-30 years, 6 males) participated in this study. METHODS: Cortico-motor excitability was assessed by monitoring the amplitude and latency of motor evoked potentials (MEPs) elicited in the right Tibialis Anterior (TA) and Soleous (SOL) muscles in response to TMS of the left motor cortex. TMS pulses were produced using a double cone coil connected to a Magstim 200 stimulator (MagStim Co. Dyfed, UK). Variations in the amplitude and latency of MEPs were measured before (i.e., baseline), during (5-min interval) and after local cooling (5 & 10-min post) of the ankle. The cooling was produced by covering the anterior and lateral aspects of the right ankle with a cold wrap (ice pack) for 20-min. Variations in the skin surface temperature were also monitored by means of an infra-red temperature gun. ANALYSIS: Paired t-tests were used to assess differences between baseline MEP values (pre-cooling) and variations measured during and after cooling. RESULTS: During cooling, the amplitude of MEPs in TA gradually decreased in parallel with the drop in skin temperature, reaching its maximum at 15 min (20% diminution on average, p < 0.05). MEP latency values in TA were correspondingly increased during cooling with significant differences being detected at 10 (p < 0.01) and 15-min (p < 0.05) cooling. After removal of the cold wrap, both MEP values and skin temperature returned to baseline by the 10th min post-application. In the SOL, similar changes were observed though the overall effect was far less important than in the TA, with large variations being noticed between individuals. No statistical differences could be detected in the SOL. CONCLUSIONS: Local cooling at the ankle selectively depresses the corticomotor excitability of the TA in parallel with the decrease in skin temperature. This depression is transitory, however, and gradually vanishes as the cooling agent is removed from the treated area. IMPLICATIONS: A period of 10-15-min should be allowed after a cold application for excitability to recover before a return to activity or engaging in exercises. KEYWORDS: motor cortex, ankle, neurophysiology. FUNDING ACKNOWLEDGEMENTS: F. Tremblay is supported by NSERC. CONTACT: francois.tremblay@uottawa.ca

ETHICS COMMITTEE: Research Ethics Committee, University of Ottawa