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J Neurophysiol. 2014 Dec 15;112(12):3219-26. doi: 10.1152/jn.00386.2014. Epub 2014 Oct 1.

The power of the mind: the cortex as a critical determinant of muscle strength/weakness.

Author information

1
Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio; Department of Biomedical Sciences, Ohio University, Athens, Ohio; Department of Geriatric Medicine, Ohio University, Athens, Ohio; clarkb2@ohio.edu.
2
Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio;
3
Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio; Office of Research, Ohio University, Athens, Ohio;
4
Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio; Department of Family Medicine, Ohio University, Athens, Ohio; and.
5
Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio; Department of Biomedical Sciences, Ohio University, Athens, Ohio; School of Rehabilitation and Communication Sciences, Ohio University, Athens, Ohio.

Abstract

We tested the hypothesis that the nervous system, and the cortex in particular, is a critical determinant of muscle strength/weakness and that a high level of corticospinal inhibition is an important neurophysiological factor regulating force generation. A group of healthy individuals underwent 4 wk of wrist-hand immobilization to induce weakness. Another group also underwent 4 wk of immobilization, but they also performed mental imagery of strong muscle contractions 5 days/wk. Mental imagery has been shown to activate several cortical areas that are involved with actual motor behaviors, including premotor and M1 regions. A control group, who underwent no interventions, also participated in this study. Before, immediately after, and 1 wk following immobilization, we measured wrist flexor strength, voluntary activation (VA), and the cortical silent period (SP; a measure that reflect corticospinal inhibition quantified via transcranial magnetic stimulation). Immobilization decreased strength 45.1 ± 5.0%, impaired VA 23.2 ± 5.8%, and prolonged the SP 13.5 ± 2.6%. Mental imagery training, however, attenuated the loss of strength and VA by ∼50% (23.8 ± 5.6% and 12.9 ± 3.2% reductions, respectively) and eliminated prolongation of the SP (4.8 ± 2.8% reduction). Significant associations were observed between the changes in muscle strength and VA (r = 0.56) and SP (r = -0.39). These findings suggest neurological mechanisms, most likely at the cortical level, contribute significantly to disuse-induced weakness, and that regular activation of the cortical regions via imagery attenuates weakness and VA by maintaining normal levels of inhibition.

KEYWORDS:

dynapenia; imagery; immobilization; muscle; strength; weakness

PMID:
25274345
PMCID:
PMC4269707
DOI:
10.1152/jn.00386.2014
[Indexed for MEDLINE]
Free PMC Article

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