RESEARCH REPORT PLATFORM PRESENTATION

LONG TERM EFFECTS OF REPETITIVE KNEE EXTENSION INDUCED BY NEUROMUSCULAR ELECTRICAL STIMULATION (R-NMES) ON MOTOR CORTICAL EXCITABILITY. Tremblay L, Arbour C, Franche M, Major K, Ouellette S; School of Rehabilitation Sciences, University of Ottawa, Ottawa, Canada

PURPOSE: It has been well established that neuromuscular electrical stimulation (rNMES) enhances the performance of innervated muscles for patients with musculoskeletal and neurological disorders. However, the effects of rNMES on brain excitability is not yet known. This project investigated the modulation of cortico motor excitability using modern technology such as transcranial magnetic stimulation (TMS) during and after prolonged application (30 mins/day X 7 days) of repetitive NMES inducing knee extension. RELEVANCE: In the re-education of motor control it is important to know the effects of NMES on the sensorimotor cortex area of the brain. PARTICIPANTS: 10 healthy male volunteers (median= 21.9±1.4 yrs) from the Faculty of Health Sciences participated in this project. METHODS: Repetitive knee extension was induced (90° to full extension without fatigue, with 10% of maximal voluntary contraction) with rNMES (Response Select©, 300 μsec, biphasic simetrical wave, 15 Hz, duty 8/8 sec, I at 2.0 X motor threshold) over the femoral nerve with a pair of rubber carbon silicone electrodes (5X8 cm). Corticospinal excitability was measured using a TMS stimulator (magstim 200©) connected to a double cone coil at 10% over motor threshold. Motor evoked potentials (MEPs) induced by the TMS were recorded (EMG) via surface electrodes placed over motor points of dominant rectus femoris muscle (RF). This electrophysiological testing was done before, immediately after 30 minutes of rNMES (during) and 30 minutes after the end of NMES (post-rNMES) at day 1 and day 7. Voluntary strength (Nicholas hand dynomometer), discomfort associated to rNMES (VAS) and muscle fatigue (Borg Fatigue Index) were also measured. ANALYSIS: Repeated non-parametric measures for a small group of subjects were used (Friedman and Welcoxon test). RESULTS: 1 session of rNMES induced a late significant facilitation of primary motor cortex excitability. In fact, MEPs increased by 77±12% 30 minutes post-rNMES and by 15±9% immediatly after rNMES compared to control values. However, a 7 day series of rNMES enhanced significantly the facilitation by 33±6% (110 ±14% vs 77±12%) in comparison to a single session of training. No change was observed immediatly after rNMES sessions at day 1 and at day 7, (15 ±9% vs. 0±4%). The muscle strength increased by 15±4% after 7 days of rNMES training. The level of comfort did not change (VAS= 3.7±0.6 after first training session and 2.8±0.4 after 7 sessions). A similar result was observed with the Borg Fatigue Index (1.2±1.4 after first training session vs 1.6±0.9 after 7 sessions). CONCLUSIONS: A delayed facilitation of the contralateral MEPs surpassing the time of application of rNMES and an increase of muscle strength following rNMES, showed an important long term effect not only peripherally but also at the sensorimotor cortex level. This training induced brain plasticity. IMPLICATIONS: These results suggest a possible implication in rehabilitation for clients suffering from motor disorders involving poor motor control and/or muscle weakness. KEYWORDS: Repetitive neuromuscular electrical stimulation, transcranial magnetic stimulation, motor cortical excitability. FUNDING ACKNOWLEDGEMENTS: Faculty of health Sciences. CONTACT: ltrembl@uottawa.ca

ETHICS COMMITTEE: University of Ottawa Research Ethics Comitee