Effect of prolonged unweighting of human skeletal muscle on neuromotor force control |
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Authors: | Brian C. Clark Joseph R. Pierce Todd M. Manini Lori L. Ploutz-Snyder |
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Affiliation: | (1) Interdisciplinary Institute for Neuromusculoskeletal Research, Department of Biomedical Sciences, Ohio University College of Osteopathic Medicine, 211 Irvine Hall, Athens, OH 45701, USA;(2) Military Performance Division, US Army Research Institute of Environmental Medicine, 15 Kansas Street—Bldg 42, Natick, MA 01760, USA;(3) Department of Aging and Geriatric Research, University of Florida College of Medicine, 1329 SW 16th Street, Room 5262, Gainesville, FL 32608, USA;(4) Department of Exercise Science, Syracuse University, 820 Comstock Ave., Room 201, Syracuse, NY 13244, USA |
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Abstract: | The purpose of this study was to determine the effect of 4 weeks of unilateral lower limb suspension (ULLS) on the fluctuations in motor output and the associated physiological changes. Subjects (n = 17) performed steady isometric plantarflexion (PF) and knee extension (KE) tasks, and KE shortening and lengthening contractions (intensity = 25% maximum). Spinal excitability of the soleus muscle was assessed via the H-reflex, muscle cross-sectional area (CSA) via MRI, along with EMG activity during the PF tasks. Following ULLS, isometric force fluctuations increased ∼12% for the PF, and 22% for the KE (P < 0.05), with no difference in the pattern of PF muscle activation (P = 0.46). The unsteadiness of lengthening KE contractions increased 25% following ULLS (P = 0.03), while KE steadiness during shortening contractions was not altered (P = 0.98). Significant correlations were observed between the percent changes in PF isometric force fluctuations and H-reflex (r = 0.49, P = 0.04), and between the PF isometric force fluctuations and PF CSA (r = −0.61, P < 0.01). These findings suggest the effects of unweighting on neuromotor performance are muscle group and contraction type dependent, and that the disuse-paradigm altering muscle CSA and spinal excitability may serve to mediate the associated loss of steadiness. Data for this project were collected in the Musculoskeletal Research Laboratory at Syracuse University. |
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Keywords: | Force control Steadiness Disuse Atrophy H-reflex |
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