(TMS) metrics were measured in the intervention and nonintervention extensor carpi radialis. Results There was 27 % motor learning and 9 % (both p < 0.001) interlimb transfer in all groups but SES added to MP did not augment learning and transfer. Corticospinal excitability increased after MP and SES when measured at rest but it increased after MP and decreased after SES when measured during contraction. No changes occurred in intracortical inhibition and facilitation. MP did not affect the TMS metrics in the transfer hand. In contrast, corticospinal excitability strongly increased after SES with MP + SES showing sharply opposite of these effects. Conclusion Motor practice and SES each can produce motor learning and interlimb transfer and are likely to be mediated by different mechanisms. The results provide insight into the physiological mechanisms underlying the effects of MP and SES on motor learning and cortical plasticity and show that these mechanisms are likely to be different for the trained and stimulated motor cortex and the non-trained and non-stimulated motor cortex. Keywords

Purpose In a previous study, we reported that a short-interval intracortical inhibition (SICI) decreases in old but not in young adults when standing on foam vs. a rigid surface. Here, we examined if such an age by task difficulty interaction in motor cortical excitability also occurs in easier standing tasks. Methods Fourteen young (23 ± 2.7 years) and fourteen old (65 ± 4.1 years) adults received transcranial magnetic brain stimulation and peripheral nerve stimulation, while they stood with or without support on a force platform. Results In the soleus, we found that SICI was lower in unsupported (35 % inhibition) vs. supported (50 %) standing ( p = 0.007) but similar in young vs. old adults ( p = 0.591). In the tibialis anterior, SICI was similar between conditions ( p = 0.597) but lower in old (52 %) vs. young (72 %) adults ( p = 0.030). Age and standing with or without support did not affect the Hoffmann reflex in the soleus. Conclusions The current data suggest that the motor cortex is involved in standing control, and that its role becomes more prominent with an increase in task difficulty.

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