FREQUENCY-DEPENDENT SOLEUS REFLEX MODULATION DURING WHOLE-BODY VIBRATION

February 12, 2026 updated by: Feride Sabırlı, Istanbul Physical Medicine Rehabilitation Training and Research Hospital

FREQUENCY- DEPENDENT MODULATION OF SOLEUS REFLEX RESPONSES DURING WHOLE BODY- VIBRATION IMPLICATIONS FOR PORPELASTIC BOBE MYOREGULATION UNDER GRAVITATIONAL LOADING

Exposure to microgravity leads to pronounced impairments in neuromuscular control, postural stability, and spinal reflex regulation that cannot be attributed to muscle atrophy alone. Rather, these deficits point to a disruption of load-dependent sensorimotor mechanisms and highlight the essential role of gravitational loading of the skeleton as a critical source of sensory input for spinal motor control.

Spinal reflex behavior during upright stance has traditionally been explained primarily by muscle spindle-mediated pathways. However, this framework does not fully account for the reflex alterations observed under conditions of altered mechanical loading, including microgravity, prolonged unloading, or exposure to vibration. In parallel, advances in bone biology have identified osteocytes within the lacuno-canalicular system as highly sensitive mechanosensors that preferentially respond to dynamic loading and changes in strain rate. This insight has given rise to the concept of bone myoregulation, in which bone-derived mechanosensory signals contribute to the modulation of spinal excitability.

A defining characteristic of this process is the poroelastic nature of bone tissue. As a fluid-saturated porous medium, bone exhibits frequency-dependent mechanical behavior, such that oscillatory loading modifies both the temporal profile and magnitude of interstitial fluid flow within the lacuno-canalicular network. As a result, loading frequency is expected to influence not only the timing of reflex responses but also their amplitude. Whole-body vibration offers a controlled experimental paradigm to probe these frequency-dependent, load-sensitive mechanisms in humans.

Accordingly, the aim of the present study was to identify the whole-body vibration frequency band that most effectively induces soleus reflex responses during quiet standing, considering both reflex latency and response amplitude. Investigators hypothesized that these responses would display frequency-dependent behavior consistent with poroelastic bone-mediated myoregulation and would be modulated by individual anthropometric characteristics, with potential implications for vibration-based countermeasures under altered gravitational loading.

Study Overview

Status

Enrolling by invitation

Conditions

Intervention / Treatment

Detailed Description

Experimental Procedure At the beginning of the experiment, participants will perform three repetitions of maximal voluntary plantarflexion (heel-rise) to determine maximal electromyographic (EMG) activity of the soleus muscle. These recordings will be used for normalization and reference purposes.

Subsequently, whole-body vibration will be applied at 13 different frequencies ranging from 25 to 49 Hz (25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, and 49 Hz). The order of vibration frequencies will be randomized for each participant to minimize order effects.

Whole-Body Vibration Protocol Participants will stand upright in an anatomically neutral position on the vibration platform and will be allowed to lightly hold the device's handrail to maintain balance without providing mechanical support. Vibration amplitude will be set at 2 mm. Each frequency condition will be applied for 15 s, with a 10 s rest period between trials. All WBV applications will be delivered using a Power Plate Pro5 device (Power Plate International Ltd., UK).

Surface Electromyography Recording Surface electromyography (sEMG) will be recorded from the left soleus muscle using bipolar Ag/AgCl electrodes (Redline®, Istanbul, Türkiye; 10-mm diameter, 4-cm interelectrode distance) aligned with the muscle fibers following appropriate skin preparation (impedance <10 kΩ). The electrodes will be placed over the lateral belly of the soleus muscle, with the ground electrode positioned on the right lateral malleolus. The sEMG signals will be amplified (×1000), band-pass filtered between 10 and 1,000 Hz, and sampled at 5,000 Hz.

EMG signals will be acquired using a CED 1902 Quad System MKIII amplifier and a CED Power 1401 MKII A/D converter and will be recorded with Spike2 software (version 7.20; Cambridge Electronic Design, UK). Signals will be stored for offline analysis. Frequency-domain analysis will be performed using fast Fourier transform (FFT) algorithms implemented in Spike2.

Study Type

Interventional

Enrollment (Estimated)

27

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Turkey (Türkiye)
    • Istanbul
      • Bahçelievler, Istanbul, Turkey (Türkiye), 34197
        • Istanbul Pmr Training Hospital

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Healthy adults aged between 20 and 45 years,
  • Absence of regular exposure to whole-body vibration (WBV) training.

Exclusion Criteria:

  • A history of intolerance to whole-body vibration,
  • Vertigo history,
  • Any medical or neurological condition that could be exacerbated by vibratory stimulation.

All participants will provide written informed consent prior to participation.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Screening
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: experimental group
Other: whole body vibration
Whole-Body Vibration Protocol Participants will stand upright in an anatomically neutral position on the vibration platform and will be allowed to lightly hold the device's handrail to maintain balance without providing mechanical support. Vibration amplitude will be set at 2 mm. Each frequency condition will be applied for 15 s, with a 10 s rest period between trials. All WBV applications will be delivered using a Power Plate Pro5 device (Power Plate International Ltd., UK).

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
1. WBV-evoked soleus reflex latency (ms)
Time Frame: 195 seconds

Reflex latency will be defined as the time interval between the onset of whole-body vibration and the onset of the reflex-related EMG response in the soleus muscle. EMG onset will be identified as the point at which the rectified EMG signal exceeds the mean baseline activity by more than two standard deviations and remains above this threshold for at least 10 ms.

This measure will be used as an index of the temporal dynamics of load-sensitive mechanotransduction, consistent with the poroelastic bone-BMR framework.
195 seconds

Other Outcome Measures

Outcome Measure
Measure Description
Time Frame
2. WBV-evoked soleus reflex amplitude (%MVC)
Time Frame: 195 seconds
Reflex amplitude will be quantified as the peak rectified EMG amplitude within the predefined reflex response window following vibration onset and normalized to the maximal voluntary contraction (MVC) obtained during heel-rise trials. Reflex amplitude will be interpreted as an indicator of the magnitude of the evoked reflex response.
195 seconds

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Istanbul Physical Medicine Rehabilitation Training and Research Hospital

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

November 30, 2025

Primary Completion (Estimated)

February 26, 2026

Study Completion (Estimated)

June 30, 2026

Study Registration Dates

First Submitted

January 26, 2026

First Submitted That Met QC Criteria

February 12, 2026

First Posted (Actual)

February 13, 2026

Study Record Updates

Last Update Posted (Actual)

February 13, 2026

Last Update Submitted That Met QC Criteria

February 12, 2026

Last Verified

February 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • 2025-78

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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