title: Increased cross-education of muscle strength and reduced corticospinal inhibition following eccentric strength training.
abstract: OBJECTIVE
  Strength training of one limb results in a substantial increase in the strength of the untrained limb, however, it remains unknown what the corticospinal responses are following either eccentric or concentric strength training and how this relates to the cross-education of strength. The aim of this study was to determine if eccentric or concentric unilateral strength training differentially modulates corticospinal excitability, inhibition and the cross-transfer of strength.
  
  
  METHODS
  Changes in contralateral (left limb) concentric strength, eccentric strength, motor-evoked potentials, short-interval intracortical inhibition and silent period durations were analyzed in groups of young adults who exercised the right wrist flexors with either eccentric (N=9) or concentric (N=9) contractions for 12 sessions over 4weeks. Control subjects (N=9) did not train.
  
  
  RESULTS
  Following training, both groups exhibited a significant strength gain in the trained limb (concentric group increased concentric strength by 64% and eccentric group increased eccentric strength by 62%) and the extent of the cross-transfer of strength was 28% and 47% for the concentric and eccentric group, respectively, which was different between groups (P=0.031). Transcranial magnetic stimulation revealed that eccentric training reduced intracortical inhibition (37%), silent period duration (15-27%) and increased corticospinal excitability (51%) compared to concentric training for the untrained limb (P=0.033). There was no change in the control group.
  
  
  CONCLUSIONS
  The results show that eccentric training uniquely modulates corticospinal excitability and inhibition of the untrained limb to a greater extent than concentric training. These findings suggest that unilateral eccentric contractions provide a greater stimulus in cross-education paradigms and should be an integral part of the rehabilitative process following unilateral injury to maximize the response.
authors.affiliation: Department of Rehabilitation, Nutrition and Sport, School of Allied Health, La Trobe University, Melbourne, Australia. Electronic address: D.Kidgell@latrobe.edu.au.
authors.forename: D J
authors.initials: DJ
authors.lastname: Kidgell
authors.affiliation: Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Australia.
authors.forename: A K
authors.initials: AK
authors.lastname: Frazer
authors.affiliation: Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Australia
authors.forename: R M
authors.initials: RM
authors.lastname: Daly
authors.affiliation: Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Rantalainen
authors.affiliation: Department of Biology and Physical Activity, University of Jyväskylä, Jyväskylä, Finland.
authors.forename: I
authors.initials: I
authors.lastname: Ruotsalainen
authors.affiliation: Department of Biology and Physical Activity, University of Jyväskylä, Jyväskylä, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Ahtiainen
authors.affiliation: Department of Biology and Physical Activity, University of Jyväskylä, Jyväskylä, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Avela
authors.affiliation: Department of Sport Exercise and Rehabilitation, Faculty of Health and Life Sciences, Northumbria University, Newcastle, UK; Water Research Group, School of Environmental Sciences and Development, Northwest University, Potchefstroom, South Africa.
authors.forename: G
authors.initials: G
authors.lastname: Howatson
mesh_terms: D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009929:Organ Size; D011712:Pyramidal Tracts / Q000502:physiology*; D055070:Resistance Training; D050781:Transcranial Magnetic Stimulation; D014953:Wrist / Q000502:physiology*
keywords: corticospinal inhibition; cross-activation; cross-transfer; ipsilateral motor cortex; recovery; strength