title: No evidence of neural adaptations following chronic unilateral isometric training of the intrinsic muscles of the hand: a randomized controlled study.
abstract: OBJECTIVE
  To test whether long-term cortical adaptations occur bilaterally following chronic unilateral training with a simple motor task.
  
  
  METHODS
  Participants (n = 34) were randomly allocated to a training or control groups. Only the former completed a 4-week maximal-intensity isometric training of the right first dorsal interosseus muscle through key pinching. Maximal strength was assessed bilaterally in four different movements progressively less similar to the training task: key, tip and tripod pinches, and handgrip. Transcranial magnetic stimulation was used to probe, in the left and right primary hand motor cortices, a number of standard tests of cortical excitability, including thresholds, intra-cortical inhibition and facilitation, transcallosal inhibition, and sensory-motor integration.
  
  
  RESULTS
  Training increased strength in the trained hand, but only for the tasks specifically involving the trained muscle (key +8.5 %; p < 0.0005; tip +7.2 %; p = 0.02). However, the effect size was small and below the cutoff for meaningful change. Handgrip and tripod pinch were instead unaffected. There was a similar improvement in strength in the untrained hand, i.e., a cross-education effect (key +6.4 %; p = 0.02; tip +4.7 %; p = 0.007). Despite these changes in strength, no significant variation was observed in any of the neurophysiological parameters describing cortico-spinal and intra-cortical excitability, inter-hemispheric inhibition, and cortical sensory-motor integration.
  
  
  CONCLUSIONS
  A 4-week maximal-intensity unilateral training induced bilaterally spatial- and task-specific strength gains, which were not associated to direct or crossed cortical adaptations. The observed long-term stability of neurophysiological parameters might result from homeostatic plasticity phenomena, aimed at restoring the physiological inter-hemispheric balance of neural activity levels perturbed by the exercise.
  
  
  BACKGROUND
  ClinicalTrials.gov identifier NCT02010398.
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Manca
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Ginatempo
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy.
authors.forename: M P
authors.initials: MP
authors.lastname: Cabboi
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Mercante
authors.affiliation: Neurology Unit, "A. Segni" Hospital, ASL n. 1, Sassari, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Ortu
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Dragone
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy.
authors.forename: E R
authors.initials: ER
authors.lastname: De Natale
authors.affiliation: Department of Physical Therapy, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel.
authors.forename: Z
authors.initials: Z
authors.lastname: Dvir
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK.
authors.forename: J C
authors.initials: JC
authors.lastname: Rothwell
authors.affiliation: Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy. deriuf@uniss.it.
authors.forename: Franca
authors.initials: F
authors.lastname: Deriu
mesh_terms: D000328:Adult; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000294:innervation / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D064797:Physical Conditioning, Human / Q000379:methods; D055070:Resistance Training / Q000379:methods
keywords: Cross education; Hand; Homeostatic plasticity; Isometric strength training; Primary motor cortex; Transcranial magnetic stimulation