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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 105/3/868    most recent 90530.2008v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Clark, B. C. Articles by Hoffman, R. L. Search for Related Content PubMed PubMed Citation Articles by Clark, B. C. Articles by Hoffman, R. L.

Neuromuscular plasticity during and following 3 wk of human forearm cast immobilization

¹Department of Biomedical Sciences, Institute for Neuromusculoskeletal Research, Ohio University, Athens, Ohio; and ²Department of Physical Therapy, SUNY Upstate Medical University, Syracuse, New York

Submitted 16 April 2008 ; accepted in final form 16 July 2008

Prolonged reductions in muscle activity results in alterations in neuromuscular properties; however, the time course of adaptations is not fully understood, and many of the specific adaptations have not been identified. This study evaluated the temporal evolution of adaptations in neuromuscular properties during and following 3 wk of immobilization. We utilized a combination of techniques involving nerve stimulation and transcranial magnetic stimulation to assess changes in central activation of muscle, along with spinal (H reflex) and corticospinal excitability [i.e., motor-evoked potential (MEP) amplitude, silent period (SP)] and contractile properties in 10 healthy humans undergoing 3 wk of forearm immobilization and 9 control subjects. Immobilization induced deficits in central activation (85 ± 3 to 67 ± 7% ) that returned to baseline levels 1 wk after cast removal. The flexor carpii radialis MEP amplitude increased greater than twofold after the first week of immobilization and remained elevated throughout immobilization and 1 wk after cast removal. Additionally, we observed a prolongation of the SP 1 wk after cast removal compared with baseline (78.5 ± 7.1 to 98.2 ± 8.7 ms). The contractile properties were also altered, since the rate of evoked force relaxation was slower following immobilization (–14.5 ± 1.4 to –11.3 ± 1.0% peak force/ms), and remained depressed 1 wk after cast removal (–10.5 ± 0.8% peak force/ms). These observations detail the time course of adaptations in corticospinal and contractile properties associated with disuse and illustrate the profound effect of immobilization on the human neuromuscular system as evidenced by the alterations in corticospinal excitability persisting 1 wk following cast removal.

electromyogram; motor cortex; motor-evoked potential; muscle; disuse