# Acute Effects of Whole-Body Vibration on Gait Kinematics in Individuals with Parkinson's Disease
## 4 Discussion  
Our results suggest that both acute WBV exposure and isometric contraction performed during HS condition could have a positive effect on gait parameters. The hypothesis that acute WBV could improve gait speed by modifying gait kinematic parameters (e.g., gait cadence and pelvic tilt) in individuals with PD was partially supported by our results. It has been known that vibration stimuli, either applied systemically or locally, significantly influence inter- and intra-muscular coordination in PD [31]. However, our results only partially support its potential benefits. Specifically, WBV did not show a significant advantage over the HS condition, suggesting that its acute effect on some of the gait parameters(i.e., propulsion and cadence) may be limited. This study represents a first step towards understanding the mechanisms underlying the effect of WBV on gait kinematics in PD. This study is the first to directly compare WBV with an isometric task performed in the absence of vibration, isolating the effects of vibration from those of isometric HS. This methodology may provide insights into whether the long-term benefits of WBV are primarily determined by the vibratory stimulus itself or by isometric contraction. [PERSON] and [PERSON]'s [32] study explored the electromyographic (EMG) activity of the vastus lateralis muscle during whole-body vibration at various frequencies. Their results demonstrated that muscle activation is highly dependent on the vibration frequency applied. Specifically, they found that a frequency of 30 Hz elicited the greatest EMG response in the vastus lateralis compared to both lower and higher frequencies. This suggests that 30 Hz may represent an optimal frequency for maximizing neuromuscular activation through mechanisms like the tonic vibration reflex. Although the original study did not directly examine 25 Hz or 35 Hz, it is possible to hypothesize their likely effects based on the observed trends. At 25 Hz, the EMG response is expected to be lower than at 30 Hz. This reduced activation could be due to suboptimal stimulation of muscle spindles and less efficient recruitment of motor units. In a clinical context, such as in patients with Parkinson's disease or other motor impairments, 25 Hz might therefore be more suitable for individuals who are sensitive to higher intensities. Conversely, at frequencies above 30 Hz, such as 35 Hz, the study suggests that EMG activity does not continue to increase and may decrease. This could be attributed to the muscle's inability to synchronize effectively with the higher frequency vibrations, leading to less efficient neuromuscular activation. For patients, this means that 35 Hz may not be as effective for eliciting strong motor responses as 30 Hz. However, it could still be valuable in certain rehabilitation scenarios, for example, to promote endurance or to provide a different neuromuscular stimulus once patients have adapted to lower frequencies. Therefore, the findings indicate that 30 Hz is likely the most effective frequency for maximizing acute muscle activation during whole-body vibration, which could translate to greater improvements in motor function, balance, and gait in patient populations. Lower frequencies like 25 Hz may be better tolerated by more fragile individuals or at the onset of therapy, while higher frequencies such as 35 Hz may offer alternative benefits but are unlikely to surpass the efficacy of 30 Hz for immediate motor activation. Thus, our WBV protocol consisted of stimuli for 1 min at 30 Hz frequency. WBV has been shown to improve overall motor function, with significant reductions in UPDRS-III scores [31], likely due to enhanced motor unit recruitment and improved inter-muscular synchronization. [PERSON] et al. [33] demonstrated that contralateral tendon vibration reduces motor unit discharge variability by 17% in the more affected limb, improving force stability during isometric contractions. This effect may be mediated by neural cross-education mechanisms at spinal or cortical level.