Anodal Transcranial Direct Current Stimulation Prolongs the Cross-education of Strength and Corticomotor Plasticity

Hendy A, Teo W, Kidgell D. Med Sci Sports Exerc. 2015;47(9):1788-1797. doi:10.1249/mss.0000000000000600

Take Home Message: The application of anodal transcranial direct current stimulation (a-tDCS) during strength training could deliver prolonged benefits in strength and neural plasticity for the contralateral arm.

A severe musculoskeletal injury can be detrimental to the self-efficacy of any athlete. One strategy to keep an athlete active and to maintain strength is to exercise the contralateral limb to elicit cross-education, which improves strength in the injured limb. Given the benefits of this type of training, it would be beneficial if we could find ways to maximize the cross-education effect. The authors conducted a double blind pseudo-randomized trial to investigate the effectiveness that anodal transcranial direct current stimulation (a-tDCS) has on the cross-education of strength and corticomotor plasticity among healthy volunteers. Twenty-four healthy volunteers (~26 years of age) were randomly divided into the three groups: 1) strength training + a-tDCS, 2) strength training + sham-tDCS, or 3) a-tDCS while resting for 2 weeks (6 sessions). Volunteers used an isokinetic dynamometer to first measure biceps brachii maximal isometric strength with the elbow flexed to 90° and the forearm supinated. After the pre-testing, the participants performed the designated treatment protocol. The strength protocol consisted of training the right biceps brachii with 4 sets of 6 repetitions of biceps curls at 80% 1-rep maximum three times per week. The study staff applied the a-tDCS to the ipsilateral motor cortex at an intensity of 1.5mA for 15 minutes during each session. The a-tDCS stimulator could provide sham treatments without the participant or researcher knowing. Transcranial magnetic stimulation was used to measure the participant’s pre-intervention and post-intervention corticomotor excitability and cross-activation of the left (untrained) biceps brachii. Immediately after the final training session, the strength training + a-tDCS group and the strength training + sham-tDCS group had strength gains (12.5% and 9.4% respectively) compared with the group with a-tDCS alone. Furthermore, both strength-training groups had increases in corticomotor excitability. After 48 hours, strength gains were retained in the strength training + a-tDCS ­group (13%) while the strength training + sham group did not retain their gains (7.6%) and were no longer different from the a-tDCS group, which had no improvements.

The authors found improvements in contralateral strength after strength training. However, only the strength-training group with a-tDCS maintained contralateral strength after 48 hours. The authors found that a-tDCS alone was not enough to improve contralateral arm strength. However, they suggested that the use of a-tDCS alone might have better results when used on patients who have motor impairments as well as older patients because they have greater deficits than these young participants do. The researchers also suggested that a-tDCS might be best for training fine, dexterous skills rather than gross motor movements, due to the addition of a-tDCS to the strength training. The addition of a-tDCS elongated the neuroplastic effects of the strength training in the participants 48 hours after the final intervention. We believe these findings to be important for the future treatment and rehabilitation of individuals who suffer from a single limb injury or impairment. Cross-education strength training is a well-researched principle in which the training of an ipsilateral limb can provide strength gains by neural adaptations to the contralateral limb. Clinicians should use cross-education strength training with patients who have an immobilized arm, and if they have a-tDCS, they may want to add it to the traditional rehabilitation protocol because it could offer a more efficient and comprehensive protocol.

Questions for Discussion: Do you think the combination of strength training and anodal transcranial direct current stimulation will become the future standard protocol for anyone with a single limb injury or impairment?
Written by: Paul Hercules, Zachary Kaptaine
Reviewed by: Jeffrey Driban

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Hendy, A., Teo, W., & Kidgell, D. (2015). Anodal Transcranial Direct Current Stimulation Prolongs the Cross-education of Strength and Corticomotor Plasticity Medicine & Science in Sports & Exercise, 47 (9), 1788-1797 DOI: 10.1249/mss.0000000000000600