Affiliations: Human Spinal Physiology Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA | Department of Physical Medicine and Rehabilitation, Kwandong University College of Medicine, Myongji Hospital, Koyang, South Korea
Note: [] Corresponding author: Yong Kyun Kim, MD, PhD, Department of Physical Medicine and Rehabilitation, Kwandong University Myongji Hospital, 697-24 Hwajung-dong, Dukyang-ku, Koyang, Kyunggi, South Korea, 412-270. Tel.: +82 31 810 5407; Fax: +82 31 969 0500; E-mail: yongkyunk@gmail.com
Abstract: Purpose: Learning a skilled movement is associated with more efficient use of subcortical motor circuits which can coordinate features of the movements such as the timing and patterns of activation of different muscles. Learning a motor skill could strengthen spinal interneuron circuits that facilitate the movement. We hypothesized that learning a simple, alternating movement would produce changes in spinal circuits that mediate reciprocal inhibition between antagonist muscles. Methods: Sixteen healthy adult subjects were trained to perform a wrist flexion and extension task to control the movement of a cursor between targets appearing on a computer display. The goal of the task was to hit the targets. Subjects practiced for 15 minutes daily until reaching the acquisition criterion. Surface EMG recordings from wrist flexor and extensor muscles showed reduced co-contraction during acquisition of the task. Results: Compared to the initial session, in the final session short-latency reciprocal inhibition was enhanced during the late-extension phase in the final session. This phase-dependent increase in short-latency reciprocal inhibition is likely to facilitate switching activation between wrist antagonistic muscles. Conclusions: Learning a motor skill can produce alterations in spinal reflex circuits that facilitate the desired movement.
