A single session of submaximal grip strength training with or without high-definition anodal-TDCS produces no cross-education of maximal force
Keywords:Cross-education, Transcranial direct current stimulation, Ipsilateral motor cortex, Short-interval intracortical inhibition, Strength training
BACKGROUND: Previous studies suggest that cross-education of strength may be modulated by increased corticospinal excitability of the ipsilateral primary motor cortex (M1) due to cross-activation. However, no study has examined the influence of bilateral TDCS of both M1 and how it affects corticospinal excitability, cross-activation and cross-education of muscle strength.
METHOD: Twelve participants underwent three conditions in a randomized crossover design: (1) submaximal grip training and single-site unilateral-high definition-TDCS (2) submaximal grip training and bilateral anodal-high definition-TDCS, and (3) submaximal grip training and sham-high definition-TDCS. Submaximal gripping task involved a single-session of unilateral training which was squeezing the transducer at 70% of maximum voluntary isometric contraction (MVIC) grip force and performing four sets of 10 isometric contractions. Anodal-high definition-TDCS was applied for 15 min at 1.5 mA over right M1 or left and right M1s, and in a sham condition. Participants were pseudorandomized to receive either single-site or bilateral M1 stimulation with each session separated by one-week. Before and after each session, MVIC force of ipsilateral and contralateral gripping, ipsilateral stimulus-response curve, short-interval intracortical inhibition, cortical silent period, intracortical facilitation, long-interval intracortical inhibition, and cross-activation were measured.
RESULTS: MVIC of the trained arm decreased by 43% (P=0.04) after training. We observed no changes in MVIC of the untrained hand and in any of the TMS measures (all P>0.05).
CONCLUSION: A single session of submaximal grip training with or without anodal-high definition-TDCS produces no cross-education of maximal grip force nor does it affect the excitability of the ipsilateral M1.
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Copyright (c) 2021 Razie Alibazi, Ashlyn Frazer, Jamie Tallent, Dawson Kidgell, Alan Pearce, Tibor Hortobágyi
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