title: The power of the mind: the cortex as a critical determinant of muscle strength/weakness.
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.
authors.affiliation: 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.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Clark
authors.affiliation: Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio;
authors.forename: Niladri K
authors.initials: NK
authors.lastname: Mahato
authors.affiliation: Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio; Office of Research, Ohio University, Athens, Ohio;
authors.forename: Masato
authors.initials: M
authors.lastname: Nakazawa
authors.affiliation: Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio; Department of Family Medicine, Ohio University, Athens, Ohio; and.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Law
authors.affiliation: 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.
authors.forename: James S
authors.initials: JS
authors.lastname: Thomas
mesh_terms: D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006225:Hand / Q000502:physiology; D006801:Humans; D007092:Imagination; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement; D053580:Muscle Strength; D018908:Muscle Weakness; D011712:Pyramidal Tracts / Q000502:physiology; D012149:Restraint, Physical; D050781:Transcranial Magnetic Stimulation; D014953:Wrist / Q000502:physiology; D055815:Young Adult
keywords: dynapenia; imagery; immobilization; muscle; strength; weakness