Acute Effects of Whole-Body Vibration on Gait Kinematics in Individuals with Parkinson’s Disease

Abstract

Background: Whole-body vibration (WBV) favors central integration and elaboration of proprioceptive stimuli, enhancing gait performance in individuals with Parkinson’s disease (PD). However, the effect of WBV on spatiotemporal gait kinematics in PD has been neglecting so far. This study aims to examine how exposure to WBV could influence kinematic parameters in PD. Methods: Gait kinematic parameters of 26 mild-stage PD participants (age: 66.7 ± 1.63 years) were measured using BTS G-Walk sensor during a 10 m walk test under three conditions—WBV, half squat without vibration (HS), and control condition (CC)—in a crossover randomized design. Results: Walking time was significantly slower (p < 0.01) in CC compared to WBV and HS, while no significant differences were observed between WBV and HS. Right leg propulsion was significantly lower in CC compared to HS (p < 0.01), with no significant differences between CC and WBV. Left leg propulsion was significantly lower in CC and WBV compared to HS (p < 0.01 and p < 0.05, respectively). Pelvic tilt was significantly lower (p < 0.05) in CC compared to WBV and HS, but no significant difference was observed between WBV and HS. Cadence was significantly lower (p < 0.05) in CC and WBV than HS. Conclusions: WBV shows promising effects on functional mobility and postural control in PD, with HS offering greater benefits. Exercise modalities should be carefully selected to enhance different gait parameters.

1. Introduction

Parkinson’s disease (PD) is a common neurodegenerative disorder affecting motor functions and leading to symptoms like tremor, rigidity, bradykinesia, and postural instability [1]. These motor impairments significantly influence gait, with reduced foot clearance, gait speed, stride length, and increased trunk inclination [2]. Moreover, gait impairments lead to an increased risk of falls, with PD individuals being nine times more likely to experience recurrent falls and five times more likely to sustain fall-related injuries compared to healthy individuals [3]. This functional decline is attributed to disruptions in the neural mechanisms that coordinate movement and balance exacerbating the challenge of managing the disease [4]. The scoping review by Russo et al. [5] emphasizes the critical role of biomechanical gait analysis in characterizing Parkinson’s disease progression and rehabilitation strategies. Clinically, improvements in neuromuscular coordination, motor unit synchronization, and postural stability are essential to improve gait performance in patients with Parkinson’s disease. These biomechanical and neuromuscular adaptations can lead to improved gait efficiency, increased gait cadence, and reduced instability, which collectively contribute to improved functional mobility and reduced risk of falls. Therefore, therapeutic interventions targeting these mechanisms, such as whole-body vibration, are promising for improving gait safety and overall quality of life in this population.

Parkinson’s disease is typically assessed using a combination of standardized clinical scales and diagnostic criteria. The Movement Disorder Society-sponsored revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) is the most widely used and validated tool for comprehensive assessment of both motor and non-motor symptoms in PD. The MDS-UPDRS consists of four parts: non-motor experiences of daily living, motor experiences of daily living, motor examination, and motor complications. It has demonstrated high internal consistency, reliability, and validity for rating the severity and progression of PD [6,7].

Another commonly used tool is the Hoehn and Yahr (HY) staging scale, which provides a simple and widely accepted method to stage the severity of PD based on motor impairment and functional disability. The HY scale correlates well with other standardized scales and with neuroimaging findings of dopaminergic loss, although it is less sensitive to subtle clinical changes [8].

Levodopa remains the primary pharmacological treatment, but long-term use can lead to motor fluctuations and side effects [9]. Consequently, complementary therapies like physical exercise (PE) and whole-body vibration (WBV) have been investigated as potential adjuvant treatments. PE has been shown to benefit both physical and psychological health by supporting neurogenesis, synaptogenesis, and angiogenesis in PD [10,11]. WBV stimuli, which involve exposing the body to mechanical vibrations, demonstrated positive effects on physical fitness in individuals with PD [12,13]. Indeed, in skeletal muscles, acute WBV stimuli induce tonic reflex contractions in the agonist muscles while relaxing the antagonists, contributing to improved motor function and enhanced muscle strength, balance, and proprioception [14,15,16]. Studies have shown that chronic exposure to WBV improves gait speed and balance in individuals with PD. For instance, Soares et al. [17] reported that WBV training increased walking speed and quality of life in individuals with PD. Similarly, Ebersbach et al. [12] showed that WBV (at 25 Hz and amplitude of 7–14 mm) combined with conventional physiotherapy improved balance and gait in individuals with PD. A recent meta-analysis by Marazzi et al. [18] confirmed the efficacy of WBV in enhancing gait performance in PD. Despite these promising findings on the chronic effects of WBV, the acute effects of WBV in this population remain less explored. Moreover, the above-mentioned study has primarily focused on the benefits of chronic WBV exposure without considering the potential influence of isometric contraction performed without vibration stimuli. This raises the question of whether the observed benefits are attributable to the vibration stimulus or the isometric contraction. Therefore, we decided to investigate the acute effects of WBV as a first step to further our understanding of its mechanisms in PD. Specifically, this study is the first to compare the effects of WBV with an isometric task performed without vibration, allowing us to isolate the contribution of vibration from that of muscle contraction. This approach may help clarify whether the chronic benefits of WBV are due to the vibration stimulus or to the isometric contraction.

However, while the benefits of chronic WBV interventions are well-documented [18], the acute effects of WBV on gait kinematics remain less understood, with few studies examining this aspect. Acute WBV can induce immediate neuromuscular and biomechanical responses (e.g., modulation of spinal reflexes, muscle activation patterns) that differ fundamentally from the structural and neural adaptations observed with long-term training [19,20]. Understanding these short-term effects is critical because it could improve WBV protocols and provide immediate and clinically meaningful improvements in gait control that support daily activities and complement chronic interventions. Therefore, studying the acute impact of WBV on gait parameters can fill an important gap in knowledge and supplement existing evidence on the chronic effects of vibration stimuli. WBV interventions have been successfully applied in other neurological conditions, like cerebral palsy, multiple sclerosis, stroke, and dementia [21,22,23,24]. Moreover, the 10 m walk test (10MWT) is a commonly used and reliable measure of gait speed in PD, with important clinical implications like predicting fall risk [25]. However, variations in test administration like static versus dynamic starts or single versus repeated trials raise questions about standardization and consistency. Lindholm et al. (2018) [25] investigated different 10 m procedures in patients with mild PD and found that variations of the procedure produced similar results with minimal measurement error. Therefore, 10MWT may be used as a simple test for clinical and research purposes in this population.

Despite these promising results, the significant variability in the vibratory parameters (frequency and amplitude) used in different studies prevents the adoption of standard protocols. Gait speed may be affected by different spatiotemporal parameters like step length, stride length, stride time, and cadence [26]. However, no data are available regarding the influence of WBV on the above-mentioned variables. Therefore, this study aims to examine how the exposure to vibration stimuli may influence spatiotemporal gait kinematics in individuals with Parkinson’s disease. By analyzing spatiotemporal gait parameters during a 10-meter walk test, the study seeks to determine whether vibration stimuli can improve gait performance, potentially mitigating Parkinson’s-related gait problems. The results may contribute to the development of non-pharmacological interventions to improve mobility and reduce the risk of falls in people with Parkinson’s disease. Our hypothesis is that acute WBV could improve gait speed by modifying gait kinematics parameters, potentially offering a complementary therapy that enhances both short- and long-term mobility.

2. Materials and Methods

2.1. Participants

A total of 26 participants (17 males and 9 females, age: 66.7 ± 7.8 years, BMI: 27.9 ± 4.1 kg/m²) with idiopathic PD were involved in this study. Participants were recruited between December 2023 and December 2024 at the Movement Disorder Centre of Magna Graecia University, Catanzaro, Italy. Inclusion criteria were diagnosis of Parkinson’s disease according to international clinical criteria [27] performed by a neurologist specialized in movement disorders, modified Hoehn and Yahr (H-Y) [8] score between 1 and 3, age >50 years old, and stable medication scheme in the last month. Exclusion criteria include contraindications to the study procedure (WBV), history of neuroleptic use, clinical features suggestive of other diseases, and significant cognitive impairment (MMSE < 24). Characteristics of participants involved in the study are shown in

Table 1. Participants’ characteristics. Data are reported as mean ± standard deviation.

Participants’ Characteristics (n = 26)
Age (years)	66.7 ± 7.8
Height (m)	1.62 ± 0.10
Body Mass (kg)	73.8 ± 13.2
BMI (kg/m2)	27.9 ± 4.1

n, participants; BMI, body mass index.

.

2.2. Experimental Procedure

All tests were performed between 11:00 am and 1:00 pm. To exclude the influence of medication, all patients were withdrawn from dopaminergic therapy overnight (>12 h). During the initial visit, each participant completed the routine initial screening at the Neuroscience Centre, including anamnesis, collection of demographic information, history of neurological disease, and assessment using Movement Disorder Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) and UPDRS-III (MDS-UPDRSME) scores [6]. If participants fell within the above-mentioned inclusion criteria, they were recruited and the gait analysis measurements were performed at the laboratory of Physical Exercise and Sport Sciences at the same institution.

Participants performed one pre-testing session (i.e., familiarization session with the experimental procedures) and one testing session. During the pre-testing session, height was measured using a Harpenden stadiometer to the nearest 0.1 cm. Body composition was measured by a bioelectrical impedance method (BIA ACCUNIQ 360, Daejeon, Republic of Korea) while participants wore minimal clothing. Finally, participants were familiarized with the experimental procedure (i.e., 10-meter walk test). The testing session consisted of three different experimental conditions performed in a random order (www.random.org) on the same day and interspersed by three-minute rest periods between each condition. During the whole-body vibration (WBV) condition, participants were in isometric half squat on a vibration platform (Pro Evolve vibrating platform (DKN, Sherman Oaks, CA, USA) with slightly bended knees (25 degrees) while receiving a vibration stimulus for 1 min at 30 Hz (g = 2.65 m/s², horizontal displacement = 0.527 mm, vertical amplitude = 3.9 mm). Knee flexion angle was measured using a goniometer, and the participants’ posture was monitored every 20 s with the goniometer to prevent incorrect positions likely caused by fatigue. Gait kinematics were then investigated during a 10-meter walk. In the half-squat (HS) condition, participants performed the same exercise protocol as the WBV condition without being exposed to the vibration stimulus. In the control condition (CC), no exercise was performed prior to the 10-meter walk test. A representation of study protocol is reported in Figure 1.

During the walking test, time was assessed using a chronometer (Casio HS-80TW-1, Casio, Tokyo, Japan), and gait parameters were assessed using a wearable inertial sensor (BTS G-Walk sensor (G-Sensor 2), BTS Bioengineering, Garbagnate Milanese, Italy; sampling frequency: 200 Hz; full scale: ±2 g; 2000°/s for the accelerometer and gyroscope, respectively) located between the L5 and S1 vertebrae, also used in a previous study conducting the same walking protocol [28]. De Ridder et al. (2019) have reported that the G-Walk is reliable for all measured spatiotemporal parameters and has excellent concurrent validity for speed, cadence, stride length, and stride duration during gait [29]. Parameters analyzed were cadence, step length of right (step length R) and left leg (step length L), stance phase of right (stance phase R) and left leg (stance phase L), swing phase of right (swing phase R) and left leg (swing phase L), stride length of right (stride length R) and left leg (stride length L), single support of right (ss R) and left leg (ss L), double support of right (ds R) and left leg (ds L), pelvic tilt, pelvic obliquity (pelvic obliq), and pelvic rotation (pelvic rot). Referring to propulsion of right leg (propulsion R) and left leg (propulsion L), the higher the propulsion index, reported in degrees, the greater the forward capacity of the patient in the single-support phase. In each test condition (WBV, HS, and CC), two attempts of the 10-meter walk were performed. The attempt performed with the shortest walking time was used for the analysis.

2.3. Data Analysis and Statistics

A priori power analysis calculation (G*Power 3.1.9.2 software, Institut für Experimentelle Psychologie, Heinrich Heine Universität, Düsseldorf, Germany) (effect size: 0.3; α = 0.05) showed that 20 participants were sufficient to achieve a statistical power of 1 − β = 0.8. The calculation of the effect size was based on a previous study with a similar sample size and population characteristics, focusing on the gait duration [30]. To ensure a conservative estimate, the effect size was approximated from 0.37 to 0.30. This approach was chosen to maintain statistical rigor while accounting for potential variability in gait measurements. All statistical analyses were performed with this sample size calculation to validate the study’s sensitivity to meaningful differences in gait parameters. Mean and standard deviation (SD) and median and interquartile range (IQR) were used for description of normally and non-normally distributed data, respectively. Statistical analysis was carried out using IBM^® SPSS statistics software version 23.0 (SPSS Inc., Chicago, IL, USA), with the significant level set at p ≤ 0.05. The normal distribution of the dependent variables was tested using the Shapiro–Wilk test. Based on this preliminary analysis, parametric tests were adopted to analyze gait kinematics parameters and the time of the 10-meter walk test. One-way ANOVA for repeated measures was conducted to detect the effects of the condition on gait parameters (walk time, cadence, step length, stance phase, swing phase, propulsion, and pelvic tilt). The assumption of sphericity for each ANOVA model was checked with Mauchly’s sphericity test. When significant differences were detected, Bonferroni post hoc analysis was run.

3. Results

A total of 61.5% of participants were in stage 1.0 whereas 11.5% and 27.0% were in stage 1.5 and 2.0, respectively, of the modified H-Y scale. A total of 22 participants underwent daily medication with LEDD (452.5 ± 331.8 mg/daily; min: 0 mg/daily, max: 1210 mg/daily), whereas 4 of them were not on any PD medication. The mean MDS-UPDRS score was 33.25 ± 14.14, while the mean UPDRS-III (MDS-UPDRS-ME) score was 16.28 ± 7.66. A significant main effect of condition was observed on walking time [(F_2,50 = 9.672, p < 0.01, η² = 0.279)]. Post hoc analysis showed that walking time was significantly (p < 0.01) longer in CC (9.7 ± 1.6 s) than in WBV (9.3 ± 1.4 s) and in HS condition (9.0 ± 1.4 s). No significant differences between WBV and HS conditions were observed for walking time (Figure 2A).

Regarding gait kinematic parameters, a significant effect of condition was observed on propulsion R [(F_2,50 = 8.491, p = 0.01, η² = 0.254)]. Post hoc analysis showed that propulsion R was significantly higher (p < 0.01) in HS (6.9 ± 1.2°) than in CC (6.3 ± 1.2°) and in WBV (6.4 ± 1.3°) conditions. No significant difference was observed on propulsion R between CC (6.3 ± 1.2°) and WBV (6.4 ± 1.3°) conditions (Figure 2B).

Moreover, a significant effect of condition was observed on propulsion L [(F_2,50 = 3.988, p < 0.05, η² = 0.138)]. Post hoc analysis showed that propulsion L was significantly higher in HS (6.9 ± 1.4°) than CC (6.4 ± 1.4°, p = 0.01) and WBV (6.5 ± 1.3°, p = 0.05) conditions. No significant difference between CC (6.4 ± 1.4°) and WBV (6.5 ± 1.3°) was observed (Figure 2C).

A significant effect of condition was observed for pelvic tilt [(F_2,50 = 3.653, p < 0.05, η² = 0.127)]. Post hoc analysis showed that pelvic tilt was significantly lower (p < 0.05) in CC (59.9 ± 24.6%) than WBV (67.7 ± 23.6%) and HS (69.6 ± 18.7%) conditions. No significant difference was observed between WBV (67.7 ± 23.6%) and HS (69.6 ± 18.7%) for pelvic tilt (Figure 2D).

A significant effect of condition was observed for cadence [(F_2,50 = 5.019, p = 0.01, η² = 0.167)]. Post hoc analysis showed that cadence was significantly higher in HS (115.6 ± 7.5 steps/min) than CC (112.3 ± 10.8 steps/min, p < 0.05) and WBV (113.5 ± 8.9 steps/min, p = 0.05). No significant difference was observed on cadence between CC (112.3 ± 10.8 steps/min) and WBV (113.5 ± 8.9 steps/min) (Figure 2E).

No significant results (p > 0.05) were observed for the other variables of interest: stance phase R (CC = 61.4 ± 2.6%, WBV = 61.4 ± 2.2%, HS = 61.1 ± 2.8%, F_2,50 = 1.997, η² = 0.074, 1 − β = 0.393), stance phase L (CC = 61.7 ± 3.1%, WBV = 61.6 ± 3.0%, HS = 61.7 ± 2.7%, F_2,50 = 0.725, η² = 0.028, 1 − β = 0.166), swing phase R (CC = 38.6 ± 2.6%, WBV = 38.6 ± 2.2%, HS = 38.9 ± 2.8%, F_2,50 = 2.027, η² = 0.075, 1 − β = 0.399), swing phase L (CC = 38.2 ± 3.1%, WBV = 38.4 ± 3.0%, HS = 38.3 ± 2.6%, F_2,50 = 0.731, η² = 0.028, 1 − β = 0.167), double-support R (ds R) (CC = 11.9 ± 2.5%, WBV = 11.4 ± 1.8%, HS = 11.4 ± 2.0%, F_2,50 = 1.978, η² = 0.073, 1 − β = 0.390), double-support L (ds L) (CC = 11.1 ± 2.6%, WBV = 11.7 ± 2.6%, HS = 11.5 ± 2.5%, F_2,50 = 0.965, η² = 0.037, 1 − β = 0.208), single-support r (ss R) (CC = 38.3 ± 3.1%, WBV = 38.4 ± 2.8%, HS = 38.1 ± 2.6%, F_2,50 = 1.233, η² = 0.047, 1 − β = 0.256), single-support L (ss L) (CC = 38.6 ± 2.8%, WBV = 38.4 ± 2.2%, HS = 38.6 ± 2.8%, F_2,50 = 0.598, η² = 0.023, 1 − β = 0.144), stride length R (CC = 1.1 ± 0.2 m, WBV = 1.1 ± 0.2 m, HS = 1.2 ±0.2 m, F_2,50 = 2.921, η² = 0.105, 1 − β = 0.545), stride length L (CC = 1.1 ± 0.2 m, WBV = 1.1 ± 0.2 m, HS = 1.2 ± 0.2 m, F_2,50 = 2.928, η² = 0.105, 1 − β = 0.546), step length R (CC = 49.5 ± 2.3%, WBV = 50.1 ± 1.4%, HS = 50.4 ± 1.6%, F_2,50 = 2.702, η² = 0.098, 1 − β = 0.511), step length L (CC = 50.5 ± 2.3%, WBV = 50.0 ± 1.4%, HS = 49.6 ± 1.6%, F_2,50 = 2.722, η² = 0.098, 1 − β = 0.514), pelvic obliq (CC = 96.4 ± 2.4%, WBV = 96.5 ± 2.6%, HS = 96.0 ± 4.0%, F_2,50 = 0.145, η² = 0.006, 1 − β = 0.71), pelvic rot (CC = 93.0 ± 7.9%, WBV = 93.8 ± 7.2%, HS = 93.8 ± 6.4%, F_2,50 = 0.538, η² = 0.021, 1 − β = 0.134).

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.

Cardinale and Lim’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. Kim 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. 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 sensori-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, Lecce 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]. However, since no significant differences were found between WBV and HS, it remains unclear whether WBV provides unique advantages in this regard or if the observed improvements are primarily due to the half-squat exercise itself. Additionally, increased muscle strength from isometric training reduces pelvic tilt and obliquity during gait, contributing to more energy-efficient movement patterns [40]. These results, although based on a different protocol [40] than ours, could explain why pelvic tilt significantly increased after the HS and WBV conditions compared to CC, although no significant difference was found between HS and WBV. Regarding the effects of vibration on pelvic tilt, Kim JH et al. [41] investigated the effects of three different vibration frequencies and pelvic positions while participants stood quietly on a WBV platform. To assess the muscle activity of the participants, electromyography analysis was conducted, indicating that WBV positively influenced muscle activity (i.e., upper trapezius, erector spinae, rectus abdominis, external oblique, gluteus maximus, rectus femoris, semitendinosus, medial gastrocnemius), with effects varying with vibration frequency and pelvic positioning. The authors recommended using higher WBV frequencies (20 Hz) to improve muscle strength and incorporating a posterior pelvic tilt during WBV, as it is shown to be significantly more effective in strengthening and training muscles related to core stability. Although based on a different intervention, this study is consistent with our findings and may explain the positive effects of the vibration on this variable [41].

The results for cadence suggest that HS was superior to both WBV and CC, with no significant differences between WBV and CC. This finding suggests that while WBV may help maintain cadence, it does not necessarily enhance it beyond what can be achieved through conventional exercise. Maintaining a consistent walking rhythm is crucial for individuals with PD, as gait irregularities increase fall risk and reduce overall mobility [18,36]. The superior performance of HS in this parameter may be attributed to the greater proprioceptive feedback and neuromuscular control facilitated by isometric movement without external vibratory stimuli [42]. Previous studies show that isometric exercises, particularly those targeting the trunk and lower limb muscles, lead to improvements in gait velocity and cadence. For instance, isometric trunk exercises significantly enhance gait speed and cadence by improving core stability and neuromuscular control, both of which are critical for maintaining rhythm and balance during walking [41,43]. These results, although based on a different protocol, could explain why cadence significantly improved after the HS condition compared to WBV and CC.

Moreover, the observed superior performance of the isometric half-squat (HS) condition in propulsion and cadence compared to whole-body vibration (WBV) suggests that sustained isometric contractions may induce neural adaptations that more effectively enhance motor output than acute WBV exposure. Isometric contractions are known to promote increased motor unit recruitment and firing rates, leading to enhanced corticospinal excitability and improved muscle activation patterns [44,45]. In contrast, WBV primarily stimulates muscle spindles and Ia afferents, eliciting reflexive muscle contractions via the tonic vibration reflex, which may produce transient neuromuscular facilitation but less pronounced voluntary motor control adaptations in the short term [15,46]. Neural adaptations to isometric training involve central nervous system plasticity, including increased cortical drive and improved synchronization of motor units [47,48], which may translate into more efficient gait propulsion and cadence improvements [49]. Therefore, the acute WBV benefits might be overridden by the more robust neural activation elicited by sustained isometric contractions.

The absence of significant differences in these metrics following whole-body vibration (WBV) intervention may be attributed to several factors, including the relatively short duration and specific parameters of the WBV protocol employed, which might have been insufficient to elicit measurable changes in these critical gait features. Furthermore, since gait abnormalities in PD are influenced by complex neurophysiological mechanisms and clinical heterogeneity, variable responses to WBV are likely, making it plausible that longer or more intensive WBV protocols could yield more pronounced effects on stride length and double-support time. Moreover, the literature presents conflicting evidence regarding the effects of WBV on gait and mobility in PD patients. Sharififar et al. (2014) [50] reported mixed findings regarding the effects of whole-body vibration (WBV) on mobility and balance in patients with Parkinson’s disease. While some studies demonstrated positive outcomes, there was no clear evidence of superiority over placebo or other active interventions. The authors identified variability in WBV parameters and intervention duration as key limitations across the included studies. Similarly, a recent meta-analysis including nine randomized controlled trials found that WBV significantly improved motor function and walking stability but did not produce statistically significant improvements in balance or activities of daily living [31].

The superior performance of HS in parameters like propulsion dx, propulsion sx, and cadence may be attributed to its ability to enhance muscle engagement, neuromuscular activation, and proprioceptive control. Unlike WBV, HS enables participants to focus more effectively on body mechanics and alignment without the potential interference of vibratory stimuli, which could mask proprioceptive feedback or induce fatigue [42,51]. Although WBV improves gait parameters in Parkinson’s disease, half squats, being low-cost and easy to perform, offer similar or greater acute benefits and may serve as a practical alternative or complement to WBV.

Finally, the effectiveness of WBV may be influenced by factors such as vibration frequency and amplitude, which can either enhance muscle activation or lead to premature fatigue [52]. Although our protocol (1 min at 30 Hz) was shown to elicit the highest reflex response in the vastus lateralis muscle during whole-body vibrations in half-squat position [32], we did not observe any additional or greater effects compared to isometric contraction. This may also depend on the nature of the study itself as it involved only an acute administration, neglecting the effect of a chronic exposure. Soares et al. [17] reported that WBV training at a frequency of 35 Hz and amplitude of 2 mm increased walking speed and quality of life in individuals with PD. Similarly, Ebersbach et al. [12] found that WBV (at 25 Hz and amplitude of 7–14 mm) combined with conventional physiotherapy improved balance and gait velocity in PD. However, these studies did not compare the effect of vibration stimuli versus isometric contraction. Moreover, the characteristics of vibratory stimulation (frequency and amplitude) largely varied among the studies, providing high heterogeneity of study protocols. Therefore, there is a need for standardized vibrational parameters (frequency, amplitude, duration) to optimize neuromuscular coordination in PD.

Our findings suggest that WBV may positively influence gait speed and pelvic tilt, and its application is well tolerated by individuals with PD who may be more susceptible to neuromuscular fatigue [53]. This study has some limitations. In our study, we have considered only participants in stages 1–2 of the H-Y scale; therefore, we cannot determine the effectiveness of the propose experimental conditions in participants with more severe Parkinson’s disease. The second limitation of our study is that as the neuromuscular activation was not evaluated, we do not have information to deeply investigate WBV response to specific neural adaptations or to elucidate the underlying mechanisms contributing to the observed functional outcomes. Recent investigations into non-pharmacological interventions for Parkinson’s disease have highlighted the potential of vibration-based therapies to enhance motor function. Kim et al. [33] reported promising acute neuromuscular benefits of contralateral tendon vibration on motor unit discharge variability and force steadiness, while also emphasizing the need for larger studies to confirm clinical relevance and long-term effects. Similarly, Zhao et al. [31] conducted a meta-analysis demonstrating significant improvements in limb function following WBV training in PD patients. However, they noted substantial heterogeneity in vibration protocols and a lack of data on sustained outcomes. These limitations underscore the necessity for future research to standardize vibration parameters, elucidate the neurophysiological mechanisms involved, and evaluate the long-term efficacy of vibration therapies. Addressing these gaps will be essential to optimize WBV as a complementary intervention to improve gait and motor control in Parkinson’s disease. Moreover, one of the limitations of our study lies in the feature selection and optimization process employed for human gait pattern recognition. Differently from Xu et al. [54], who proposed a novel method leveraging metaheuristic optimization algorithms for optimal feature selection, in our study we did not implement this advanced and systematic methodology. Indeed, in their study, Xu et al. [54] identified relevant gait parameters using a sample of healthy athletes. Since gait kinematics may be markedly different between healthy and pathological individuals, the identified gait parameters may not be used in our study. Similarly, the application of Xu et al.’s [54] algorithm to our sample might produce questionable results given the limited sample size. Future studies on the larger sample of patients with Parkinson’s disease are warranted to identify distinctive kinematics and kinetics parameters in this population.

5. Conclusions

Although whole-body vibration (WBV) shows potential in enhancing functional mobility and postural control in individuals with Parkinson’s disease (PD), isometric exercises such as half squats (HSs) demonstrate superior benefits in key kinematic parameters (propulsion right, propulsion left, and cadence). This highlights the importance of selecting appropriate exercise modalities in rehabilitation, with HS representing a cost-effective and accessible option for acutely improving gait performance in PD patients.

While WBV provides improvements over conventional therapy, its benefits are not significantly greater than those observed with HS. Therefore, HS may serve as a practical alternative or adjunct to more resource-intensive interventions like WBV, particularly in clinical and community settings with limited equipment.

Future research should focus on longitudinal, randomized controlled trials to investigate the chronic effects of combined WBV and HS interventions. Such studies should assess not only kinematic outcomes but also quality of life measures to better understand the potential for neuroplastic adaptations, muscle strengthening, and improvements in motor control and the dose–response relationship of HS. This evidence could inform optimized rehabilitation protocols for individuals with Parkinson’s disease.