title: Cast immobilization increases long-interval intracortical inhibition.
abstract: Immobilization reduces muscle performance, and despite these performance losses being associated with neural impairments little is known regarding adaptations in cortical properties. We utilized transcranial magnetic stimulation to assess changes in flexor carpi radialis (FCR) intracortical facilitation (ICF), and short- and long-interval intracortical inhibition (SICI and LICI) in healthy humans undergoing 3 weeks of immobilization. Measurements were obtained at rest and during contraction (15% intensity). Central activation and the Hoffman reflex (H-reflex) were also assessed. Strength decreased 43.2% +/- 6.1% following immobilization, and central activation also decreased (97.5% +/- 2.4% to 73.2% +/- 8.3%). No changes in ICF, SICI, or LICI were observed at rest; however, LICI was increased during contraction (67.5% +/- 6.9% to 53.1% +/- 6.7% of unconditioned response). The increase in LICI correlated with the loss of strength (r = -0.63). The H-reflex increased following immobilization. These findings suggest that immobilization increases intracortical inhibition during contraction, and this increase is primarily mediated by GABA(B) receptors.
authors.affiliation: Institute for Neuromusculoskeletal Research, Ohio University, Athens, Ohio 45701, USA. clarkb2@ohio.edu
authors.forename: Brian C
authors.initials: BC
authors.lastname: Clark
authors.forename: Janet L
authors.initials: JL
authors.lastname: Taylor
authors.forename: Richard L
authors.initials: RL
authors.lastname: Hoffman
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Dearth
authors.forename: James S
authors.initials: JS
authors.lastname: Thomas
mesh_terms: D002370:Casts, Surgical; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006225:Hand / Q000294:innervation / Q000502:physiology; D006801:Humans; D007103:Immobilization / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D014953:Wrist / Q000294:innervation / Q000502:physiology; D055815:Young Adult