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In healthy populations, balance training can improve the performance in trained tasks, but may have only minor or no effects on non-trained tasks. Consequently, therapists and coaches should identify exactly those tasks that need improvement, and use these tasks in the training program and as a part of the test battery that evaluates the efficacy of the training program. Generic balance tasks-such as one-leg stance-may have little value as overall balance measures or when assessing the efficacy of specific training interventions.

Highlights-Ego depletion and mental fatigue impair subsequent endurance performance-The duration of the mental effort task doesn't predict the magnitude of impairment-The effect is higher on isolation than whole-body tasks-The effect is higher when the person-situation fit is low-This effect should not be seen only through the "fatigue" prism but also as "value"

Key points• Botulinum neurototoxin type A (BoNT-A) is known to block central synapses after muscular injection due to retrograde transport in animal models.• BoNT-A-induced changes in the human CNS activity have been attributed so far to indirect mechanisms involving peripheral afferent inputs modified after muscular injection.• The question of a possible direct central action of BoNT-A in humans was further addressed by investigating the modification of spinal recurrent inhibition in stroke patients after BoNT-A muscular injection.• Recurrent inhibition from soleus motor axons to motoneurones supplying quadriceps was depressed after BoNT-A injection in ankle plantarflexors.• BoNT-A, through retrograde transport, affects spinal synaptic transmission in humans.Abstract The natural target of the botulinum neurototoxin type A (BoNT-A) is the neuromuscular junction. When injected into a muscle, BoNT-A is internalized by motoneurone terminals where it functions as an endopeptidase, cleaving protein components of the synaptic machinery responsible for vesicle docking and exocytosis. As a result, BoNT-A induces a characteristic flaccid paralysis of the affected muscle. In animal models, BoNT-A applied in the periphery can also influence central activity via retrograde transport and transcytosis. An analogous direct central effect in humans is still debated. The present study was designed to address whether BoNT-A modifies the activity of the spinal recurrent inhibitory pathways, when injected at muscular level, in humans. To avoid methodological bias, the recurrent inhibition from an injected muscle (soleus) was investigated on an untreated muscle (quadriceps), and stimulation parameters (producing recurrent inhibition) were monitored on a third non-injected muscle but innervated by the same nerve as the soleus (flexor digitorum brevis). The experiments were performed on 14 post-stroke patients exhibiting spasticity in ankle plantarflexors, candidates for BoNT-A. One month after BoNT-A, the level of recurrent inhibition was depressed. It is suggested that the depression of recurrent inhibition was induced by BoNT-A, injected peripherally, through axonal transport and blockade of the cholinergic synapse between motoneurone recurrent collaterals and Renshaw cells.

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Slackline training is a challenging and motivating type of balance training, with potential usefulness for fall prevention and balance rehabilitation. However, short-term slackline training seems to elicit mostly task-specific performance improvements, reducing its potential for general fall prevention programs. It was tested whether a longer duration slackline training (three months, 2 sessions per week) would induce a transfer to untrained tasks. Balance performance was tested pre and post slackline training on the slackline used during the training, on a slackline with different slack, and in 5 different non-trained static and dynamic balance tasks (N training = 12, N control = 14). After the training, the training group increased their performance more than the control group in both of the slackline tasks, i.e. walking on the slackline (time × group interaction with p < 0.001 for both tasks). However, no differences between groups were found for the 5 non-trained balance tasks, only a main effect of time for four of them. The long-term slackline training elicited large task-specific performance improvements but no transfer to other non-trained balance tasks. The extensive slackline training that clearly enhanced slackline performance did not improve the capability to keep balance in other tasks and thus cannot be recommended as a general fall prevention program. The significant test-retest effect seen in most of the tested tasks emphasizes the need of a control group to adequately interpret changes in performance following balance training.

Hanna-Boutros B, Sangari S, Karasu A, Giboin LS, MarchandPauvert V. Task-related modulation of crossed spinal inhibition between human lower limbs. J Neurophysiol 111: 1865-1876, 2014. First published February 5, 2014 doi:10.1152/jn.00838.2013.-Crossed reflex action mediated by muscle spindle afferent inputs has recently been revealed in humans. This raised the question of whether a complex spinal network involving commissural interneurons receiving inputs from proprioceptors and suprasegmental structures, as described in cats, persists in humans and contributes to the interlimb coordination during movement. First, we investigated the neurophysiological mechanisms underlying crossed reflex action between ankle plantar flexors and its corticospinal control from primary motor cortex. Second, we studied its modulation during motor tasks. We observed crossed inhibition in contralateral soleus motoneurons occurring with about 3 ms central latency, which is consistent with spinal transmission through oligosynaptic pathway. The early phase of inhibition was evoked with lower stimulus intensity than the late phase, suggesting mediation by group I and group II afferents, respectively. The postsynaptic origin of crossed inhibition is confirmed by the finding that both H-reflex and motor-evoked potential were reduced upon conditioning stimulation. Transcranial magnetic stimulation over ipsilateral and contralateral primary motor cortex reduced crossed inhibition, especially its late group II part. Last, late group II crossed inhibition was particularly depressed during motor tasks, especially when soleus was activated during the walking stance phase. Our results suggest that both group I and group II commissural interneurons participate in crossed reflex actions between ankle plantar flexors. Neural transmission at this level is depressed by descending inputs activated by transcranial magnetic stimulation over the primary motor cortex or during movement. The specific modulation of group II crossed inhibition suggests control from monoaminergic midbrain structures and its role for interlimb coordination during locomotion.H-reflex; TMS; commissural interneurons; corticospinal; locomotion SEVERAL SPINAL PATHWAYS INVOLVING commissural interneurons mediate crossed reflex actions from proprioceptors. In cat lumbar cord, these pathways are closely interconnected and incorporated into complex networks coordinating muscle activity on both sides (Jankowska 2008).

This study demonstrated that short-term strength training induces specific neuroplasticity for the trained task only. The fact that MEPs were lower but H-reflex amplitudes remained unchanged at the onset of the trained tasks suggests that strength training elicited neuroplasticity at supraspinal level that most likely reflect an improved task-specific corticospinal efficiency.