Immediate Effect of Focal Mechanical Vibration on Anticipatory Postural Adjustments during Gait Initiation

다국어 초록 (Multilingual Abstract)

Anticipatory postural adjustments (APAs) are feedforward mechanisms that prepare the body for movement-induced perturbations during the transition from standing to walking. Focal mechanical vibration (FMV) has been used to modulate the proprioceptive input and motor control, but the differential effects of segmental vibration along the anterior body segment on gait initiation are unclear. This study examined the effects of FMV applied to three distinct anterior body segments on the APA characteristics and first- step kinematics during gait initiation. Young adults were assigned randomly to three vibration site groups: shank, thigh, and chest. The participants performed gait initiation under three conditions: no vibration, cessation (vibration applied for 60 seconds followed by immediate cessation at movement onset), and continuous (vibration maintained throughout movement). The kinematic data were collected using a motion capture system at 100 Hz, and the kinetic data were obtained from force platforms at 1,000 Hz. The APA parameters (distance, duration, and speed) were measured across three phases: SOF-APA (start of frame to anticipatory postural adjustment), APA-RTO (anticipatory postural adjustment to right toe-off), and RTO-LTO (right toe-off to left toe-off). The spatiotemporal parameters during the first step were also analyzed. The analysis showed significant interaction effects between the vibration site and condition on SOF-APA duration and center of pressure displacement speed (p < 0.05). The chest group showed significant reductions in SOF-APA duration in cessation and continuous conditions compared to no vibration (p < 0.05). The shank group showed a reduced duration in the continuous condition compared to cessation (p < 0.05). The chest group showed a higher CoP speed during continuous vibration compared to cessation and no vibration conditions (p < 0.05). No significant effects were observed in the APA-RTO and RTO-LTO phases. The main effects of the conditions were found for the step length, with both vibration conditions showing lower values than no vibration (p < 0.05). The temporal parameters, including swing time and stance time, remained unaffected by vibration. These results suggest that proprioceptive augmentation through anterior body segment vibration modulates the APA performance in a segment-dependent manner, with proximal trunk stimulation showing the most pronounced improvements. The limited response to shank vibration in the cessation condition, compared to the consistent effects in the chest group, reflects segment-dependent sensory processing, where trunk inputs are prioritized over distal proprioceptive signals during whole-body movement preparation. The reduction in the spatial parameters with preserved temporal characteristics reflects a stability-prioritizing adaptive strategy. This study provides evidence that trunk-focused FMV may be an effective intervention for enhancing gait initiation in populations with motor control impairments.

목차 (Table of Contents)

• Ⅰ. Introduction 1
• 1. Neurophysiological Foundations of Anticipatory Postural Adjustments 3
• 2. Focal Mechanical Vibration: Mechanisms and Applications 5
• 3. Current Evidence and Research Gaps 7
• 4. Study Objectives 8
• Ⅱ. Methods 9
• 1. Study Design and Participants 9
• 2. Experimental Setup 10
• 2.1. Motion Analysis System 10
• 2.2. Force Plates 12
• 2.3. Focal Mechanical Vibration System 13
• 2.3.1. Precise Vibrator Placement Protocol 13
• 3. Experimental Protocol 15
• 4. Data Processing and Analysis 17
• 4.1. Outcome Measures Definition 17
• 4.1.1. Anticipatory Postural Adjustment (APA) Parameters 17
• 4.1.2. Spatiotemporal Parameters (First Step) 17
• 4.2. Signal Processing and Phase Identification 19
• 5. Statistical Analysis 20
• Ⅲ. Results 21
• 1. Participant Characteristics 21
• 2. Anticipatory Postural Adjustment Parameters 22
• 2.1. SOF-APA Phase 22
• 2.2. APA-RTO and RTO-LTO Phases 26
• 3. Spatiotemporal Parameters 29
• Ⅳ. Discussion 31
• 1. Proximal Superiority in APA Modulation 32
• 2. Effects of Vibration Timing on APA Characteristics 33
• 3. Stability-Mobility Trade-off and Adaptive Strategies 34
• 4. Limitations and Future Directions 35
• V. Conclusion 36
• References 39