Abstract
Motor cortical contribution was shown to be important for balance control and for ballistic types of movements. However, little is known about the role of cortical inhibitory mechanisms and even less about long(er)-term adaptations of these inhibitory processes. Therefore, the aim of the present study was to investigate the role of intracortical inhibition before and after four weeks of explosive or balance training. Two groups of subjects participated for four weeks either in an explosive training programme of the plantar flexor muscles or in a balance training programme on unstable devices. Adaptations in short-interval intracortical inhibition (SICI) were assessed by applying paired-pulse TMS to the soleus muscle during dynamic plantar flexions, balance perturbations and at rest. Furthermore, SICI was assessed for the untrained tibialis anterior muscle. The results show task-, muscle- and group-specific adaptations in SICI after the training (p=.021) with significantly increased SICI after balance training in the balance task and decreased SICI after explosive training in the ballistic task. The training also caused task- and group-specific behavioural adaptations indicated by improved balance performance after balance training and increased ballistic performance after explosive training. There were no changes in SICI when measured at rest or in the untrained tibialis anterior muscle. This study shows that long(er)-term training improves the ability to modulate cortical inhibitory processes in a task- and muscle-specific manner.
Highlights
Motor learning is the result of plastic changes within the neural system, and it is well known that the primary motor cortex plays a crucial role (Classen, Liepert, Wise, Hallett, & Cohen, 1998; Lotze, Braun, Birbaumer, Anders, & Cohen, 2003; Muellbacher, Ziemann, Boroojerdi, Cohen, & Hallett, 2001; Muellbacher et al, 2002)
Depending on the rate of torque development (RTD) and balance performance of the pre‐test, subjects were randomly assigned into two groups from which one group performed four weeks of explosive training (ET) while the second group participated in four weeks of balance training (BT)
The results demonstrated a task‐ and group‐specific adaptation in short‐interval intracortical inhibition (SICI) as post hoc tests showed that there was a significant increase in SICI during the balance perturbations after balance training programme (BT) (15.6 ± 5.5 vs. 35.0 ± 6.6%, p = .01) while explosive training programme (ET) did not show a significant change in SICI (20.5 ± 5.7% vs. 28.7 ± 6.9%, p = .32; Figure 2b,d)
Summary
Motor learning is the result of plastic changes within the neural system, and it is well known that the primary motor cortex plays a crucial role (Classen, Liepert, Wise, Hallett, & Cohen, 1998; Lotze, Braun, Birbaumer, Anders, & Cohen, 2003; Muellbacher, Ziemann, Boroojerdi, Cohen, & Hallett, 2001; Muellbacher et al, 2002). Perez et al (2004) showed that SICI was significantly reduced after 32 min of motor skill training, but unaffected by nonskill or passive training. To test for group‐ and task‐specific adaptations in SICI (paired‐pulse TMS) and corticospinal excitability (single‐pulse TMS) after the training, a three‐way repeated measures ANOVA with factors time (pre, post), condition (balance perturbation, plantar flexion) and group (ET, BT) was calculated. To evaluate changes in motor behaviour, the Z‐transformations (Kleinbaum, Kupper, Azhar, & Muller, 1978; Taube, Leukel, et al, 2008) were used before comparing results of the balance and strength tests by calculating a three‐way ANOVA with factors time (pre, post), condition (balance performance, RTD) and group (ET, BT). The ANOVA revealed no significant condition (F1,22 = 1.6, p = .22, η2 = 0.068) and no time*group effect (F1,22 = 0.13, p = .73, η2 = 0.006).
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