title: Mirror Training Augments the Cross-education of Strength and Affects Inhibitory Paths.
abstract: Unilateral strength training strengthens not only the muscles on the trained side but also the homologous muscles on the untrained side; however, the magnitude of this interlimb cross-education is modest. We tested the hypothesis that heightened sensory feedback by mirror viewing the exercising hand would augment cross education by modulating neuronal excitability.
  
  
  
  Healthy adults were randomized into a mirror training group (MG, N = 11) and a no-mirror training group (NMG, N = 12) and performed 640 shortening muscle contractions of the right wrist flexors at 80% maximum voluntary contraction (MVC) during 15 sessions for 3 wk. Maximal strength and specific transcranial magnetic stimulation metrics of neuronal excitability, measured in the mirror and no-mirror setup at rest and during unilateral contractions at 60% MVC, were assessed before and after the strength intervention.
  
  
  
  Trained wrist flexor MVC increased 72% across groups, whereas cross-education was higher for the MG (61%) than NMG (34%, P = 0.047). The MG showed a reduction (15%-16%) in the contralateral silent period duration measured from the contracting left-untrained flexor carpi radialis, whereas the NMG showed an increase (12%, P ≤ 0.030). Interhemispheric inhibition, measured from the trained to the untrained primary motor cortex, increased in the MG (11%) but decreased in the NMG (15%) when measured in the mirror setup at rest (P = 0.048). Other transcranial magnetic stimulation measures did not change.
  
  
  
  Viewing the exercising hand in a mirror can augment the cross-education effect. The use of a mirror in future studies can potentially accelerate functional recovery from unilateral impairment due to stroke or upper limb fracture.
authors.affiliation: 1University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Groningen, THE NETHERLANDS; 2Faculty of Health and Life Sciences, Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle-upon-Tyne, UNITED KINGDOM; 3Motor Control Laboratory, Department of Kinesiology, Pennsylvania State University, State College, PA; 4University School of Physical Education, Wroclaw, POLAND; and 5Water Research Group, School of Biological Sciences, North West University, Potchefstroom, SOUTH AFRICA.
authors.forename: Tjerk
authors.initials: T
authors.lastname: Zult
authors.forename: Stuart
authors.initials: S
authors.lastname: Goodall
authors.forename: Kevin
authors.initials: K
authors.lastname: Thomas
authors.forename: Stanislaw
authors.initials: S
authors.lastname: Solnik
authors.forename: Tibor
authors.initials: T
authors.lastname: Hortobágyi
authors.forename: Glyn
authors.initials: G
authors.lastname: Howatson
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010525:Peripheral Nerves / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D055070:Resistance Training / Q000379:methods*; D050781:Transcranial Magnetic Stimulation; D014953:Wrist / Q000502:physiology