# Acute Effects of Whole-Body Vibration on Gait Kinematics in Individuals with Parkinson's Disease
## 4 Discussion
At the intra-muscular level, localized vibration (60 Hz) applied to lower limb muscles reduced the sway area of the center of pressure [34], possibly indicating improved sensor-motor integration process due to increased proprioceptive input from muscle spindles. We suppose that the increased proprioceptive input of muscle spindles could improve dynamic balance by allowing greater stability during the load-accepting phase as the foot stands in the gait. This would also allow load to be transferred more quickly from one stance to the other making the walk faster, thus improving gait speed. Considering the above-mentioned findings, we may hypothesize that WBV exposure may improve gait performance in the PD population. However, there is no clear evidence of a PD symptom-reducing effect of WBV compared with control conditions. Only a few studies showed significant group differences for mobility and motor symptoms [12; 35]. Therefore, the overall effects of vibration therapy on PD remain somewhat inconsistent [36]. The observed improvement in walking time in both WBV and HS conditions compared to the control condition (CC) is consistent with previous research indicating that WBV may enhance gait speed and neuromuscular activation in individuals with PD [18; 36]. However, the lack of significant differences between WBV and HS suggests that WBV stimuli do not provide additional advantages over isometric contraction in this context, contrary to our initial hypothesis. This finding may be attributed to the nature of the exercises performed, as previous studies have noted that WBV's efficacy can be influenced by factors like exercise modality and vibration frequency [13; 36]. However, [PERSON] et al. [37] investigated the acute effects of acute WBV exposure on motor units' behavior. Their data showed no significant changes in motor unit recruitment or derecruitment thresholds, discharge rates, or interspike interval variability following any of the tested conditions. These results indicate that acute exposure to WBV, as well as static standing or control conditions, did not alter the behavior of voluntarily activated motor units during submaximal isometric contractions. This suggests that short-term WBV, under the current protocol, does not significantly affect neuromuscular control at the level of individual motor units. While WBV may influence other aspects of muscle performance, its acute effects on motor unit properties appear limited. Furthermore, although using a different protocol, a previous study [12] reported a positive effect on gait velocity following a chronic whole-body vibration intervention lasting three weeks. Regarding propulsion, HS showed an improvement compared to both WBV and CC, particularly in right leg propulsion (Propulsion R) and left leg propulsion (Propulsion L). These findings indicate that engaging in isometric half squats may promote better propulsion mechanics than WBV, reinforcing the notion that muscle engagement during voluntary movements plays a crucial role in improving functional mobility in individuals with PD [18; 38]. Enhanced strength in the hip extensors and knee extensors through isometric training facilitates symmetrical force generation between the right and left legs, improving overall propulsion mechanics. This is particularly beneficial for dynamic tasks like walking or running [37; 39]. Furthermore, training at longer muscle lengths improves neuromuscular activation and tendon function, supporting better force transfer during the propulsion phases of gait [39]. It is likely that isometric training facilitates force generation by improving overall propulsion, which would be consistent with our findings of improved propulsion after the HS condition. Pelvic tilt analysis further underscores the benefits of both WBV and HS over CC, suggesting that these interventions may enhance postural control and stability. Given that postural instability is a major challenge for individuals with PD, the ability of WBV to facilitate pelvic alignment and balance control is noteworthy [36].