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NCT Number: NCT07408570

FREQUENCY-DEPENDENT SOLEUS REFLEX MODULATION DURING WHOLE-BODY VIBRATION

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.

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Key information

Conditions

Healthy Adult Whole Body Vibration

Age range

20 year–45 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Istanbul Pmr Training Hospital

Bahçelievler, Istanbul, 34197, Turkey (Türkiye)

About this study

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.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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.

Treatment and study plan

Whole body vibration

Other

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).

Primary outcomes

  1. 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.

Other outcomes

  1. 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.

Sponsors and collaborators

Lead sponsor

Istanbul Physical Medicine Rehabilitation Training and Research Hospital

Other Gov

Registry information

Official study title

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

Important dates

Study start
2025
Primary completion
2026
Study completion
2026
First posted
Feb 13, 2026
Registry last updated
Feb 13, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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