## 4 Discussion
Experiments carried out on the muscle-tendon unit have shown that muscle vibration is a strong proprioceptive stimulus that reaches both the primary somatosensory (SI) and motor (M1) cortices directly [88] and that the frequency exerts a dependent effect on the Ia afferent firing rate that is reflected in differential frequency-dependent effects on corticospinal motor neuron excitability [89]. These neural mechanisms explain the benefits of acute and chronic WBV intervention on muscle strength, power, gait, and balance [33; 34; 84; 90]. Furthermore, these enhancements can be further demonstrated by the enhanced activation and synchronization of MUs [30] and the enhanced sensorimotor integration that results from the repeated stimulation of muscle spindles and Ia afferents [84; 85]. Postural control and intermuscular coordination are likely to be more efficient during dynamic tasks as a result of this neuromuscular tune-in [31]. Furthermore, these enhancements can be further demonstrated by the enhanced activation and synchronization of MUs [30] and the enhanced sensorimotor integration that results from the repeated stimulation of muscle spindles and Ia afferents [84; 85]. Postural control and intermuscular coordination are likely to be more efficient during dynamic tasks because of this neuromuscular tune-in [31]. The MRI results of the participant indicate that there were no reductions in CNS injury. This is consistent with a recent study by [PERSON] et al. [91], in which the injury of MS did not change, despite those subjects showing improvements in motor assessment. This is consistent with the specific nature of the treatment, which is not disease-modifying but supportive of recovery. Previous studies suggest that such improvements in individuals with MS following exercise may depend on increased serum levels of specific hormones [24]. Our results report an important increase in GH (827% two hours after the end of a single WBV session) and an increase in testosterone (of 8% after one hour). It has been suggested that in MS, hormones like GH are involved in the neuro-reparative process; in fact, GH exerts trophic effects on neuronal regeneration in peripheral and CNS, stimulating the protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells. In addition, GH favors the survival of myelin and CNS cells, inhibiting apoptosis [92,93]. Furthermore, the effect of GH could be mediated by or be overlapped with that of other hormones, such as testosterone [92]. In this regard, [PERSON] et al. [94] suggested that exogenous testosterone has potential neuroprotective effects in men with RRMS because of its ability to increase the grey matter in the frontal cortex [92]. Furthermore, our results show a reduction in the cortisol level (36% after 2 h), which is consistent with other studies [95,96,97,98]. This result could have specific relevance because people with multiple sclerosis exhibit a failure to suppress cortisol release, correlated with high scores on depression and anxiety scales [98]. Interestingly, we also observed an increased testosterone-cortisol ratio post WBV session as the time under tension, in the isometric high squat position, was not brief (each repetition lasted 30-60 s \(\times\) total of 7-10 reps) [39]. These hormonal changes may contribute to functional improvements by modulating neurotransmission and enhancing neuroplasticity. Elevated levels of GH and testosterone, with a decrease in cortisol, may help establish a favorable neuroendocrine environment that enables the repair of myelin and the restoration of motor function in individuals with MS [24,88,89]. Finally, the WBV effects that we found and the creatine kinase concentrations are in line with those induced by applying high-intensity eccentric exercise associated with prolonged muscle damage [39].