Whole-body Vibration Induces a Short or Long Latency Muscular Reflex
Condition: Effects of Vibration
Study type: Interventional

Summary: 
      Aim: Hypothesis of this study was that WBV activates different receptors or reflex pathways
      depend on vibration intensity. Aim of this study was to test this hypothesis.

      Methods: This study was conducted on 11 healthy adults. WBV was applied at various
      frequencies and amplitudes. The right soleus T-reflex latency was determined before and
      during WBV. WBV-IMR latency of the right soleus was determined using two different vibration
      intensity: weak vibration and powerful vibration. T-reflex latency and WBV-IMR latency were
      determined by using cumulated average method.
    

Detailed description: 
      Aim: Whole-body vibration (WBV) induces a reflex response in muscles. The physiological
      mechanisms underlying this reflex have been explained by activating muscle spindles
      (stretch-induced reflex) or osteocytes (bone myoregulation reflex). WBV-induced muscular
      reflex (WBV-IMR) latency was reported to be significantly longer than latency of T-reflex as
      a stretch-induced reflex or nearly equal to T-reflex latency in the literatures. Hypothesis
      of this study was that WBV activates different receptors or reflex pathways depend on
      vibration intensity. Aim of this study was to test this hypothesis.

      Methods: 2.1. Participants

      Eleven young, healthy and right hand dominant male adult volunteers were included in this
      study. The mean age of the participants was 25.4 ± 4.7 years, mean body height was 176.5 ±
      6.7 cm and mean body weight was 77.8 ± 13.8 kg. All volunteers gave written informed consent
      to the experimental procedures, which were in accordance with the Declaration of Helsinki and
      were approved by the local ethics committee (Yeditepe University Medical Faculty Clinical
      Research Evaluation Committee, Istanbul; 2016/564 ).

      2.2. Procedure Prior to the induction of WBV, control T-reflex recordings were elicited and
      then the participants completed a 15-s trial WBV protocol to familiarize themselves with the
      procedure. Following the control T-reflex recordings, the trial protocol and a 15-s rest, the
      participants received three set of WBV and T-reflex stimuli during WBV. A weak vibration was
      applied in the first set. In next sets, a moderate and strong vibration were applied,
      respectively. Vibration characteristics of three sets was given in Table 1. A WBV set
      consisted of four vibration periods, each lasting for 60 s, with 5-s rest intervals between
      periods. Within each set, WBV frequencies of 25, 29, 33, and 37 Hz were delivered The surface
      electromyography (SEMG) and accelerometer data were obtained while the participants stood
      upright on the vibration platform with the knees in extension. The participants were
      barefooted and stood directly on the vibration platform. The whole plate oscillated with a
      linear movement upward and downward. Two WBV devices (Power-Plate®Pro5, PowerPlate®
      International, Ltd. London, UK) were used in the present study. One of them was used for
      applying the moderate and strong vibration. The other WBV device was modified to attenuate
      vibration intensity and used for applying the weak vibration.

      2.3. Data Recordings The recordings of both T-reflex and WBV-IMR were acquired using SEMG.
      The Ag/AgCl electrodes (KENDALL®Covidien) with a disc radius of 10 mm were placed 20 mm apart
      on the right soleus muscle belly on shaved skin that had been cleaned with alcohol in
      accordance with the recommendations of the Surface ElectroMyoGraphy for the Non-Invasive
      Assessment of Muscles (SENIAM) project (Hermens et al., 2000). The ground electrode was
      placed on the lateral malleolus. The sampling frequency was selected as 10 kHz.

      A very light (2.9 g) triaxial MEMS piezoaccelerometer (LIS344ALH, full-scale of ± 6 g, linear
      accelerometer, ECOPACK®) was taped to the participant's right Achilles tendon to determine
      the timing of the onset of the mechanical stimulus for the T-reflex and to measure stroke
      intensity of reflex hammer to Achilles tendon (Achilles accelerometer). Similar
      accelerometers fixed to the WBV platforms to determine the timing of the onset of the
      mechanical stimulus for the WBV-IMR (platform accelerometers). Acceleration unit used in this
      study was m/s2.

      A custom-made reflex hammer tapped the right Achilles tendon just caudal to the accelerometer
      with a force of about 19.6 N. Before vibration and in each vibration session, the Achilles
      tendon was tapped ten times with approximately 3-s intervals between taps.

      2.4.Data processing SEMG and accelerometer data were recorded using a PowerLAB® data
      acquisition system (ADInstruments, Oxford, United Kingdom) and the data were analyzed offline
      using the LabChart7® (ver 7.3.7, ADInstruments, Oxford, United Kingdom) software. A sampling
      frequency of 10 kHz was used. All accelerometer recordings were filtered with high-pass
      filter set at 5 Hz. All EMG recordings were filtered using a band pass filter from 60 to 500
      Hz.

      The maximum peak-to-peak (PPmax) amplitudes of T-reflex were determined for each vibration
      session. The amplitude of WBV-IMR was expressed as the Root Mean Square (RMS). The PPmax
      amplitude of T-reflex and RMS amplitude of WBV-IMR recorded during the strong WBV were used
      to normalize of the PPmax amplitude of T-reflex and RMS amplitude of WBV-IMR recorded before
      WBV or during weak and moderate WBV.

      In the present study, reflex latency was defined as the time between the onset of the
      mechanical stimulus and the onset of the EMG spike on the cumulated average trace, both of
      which were determined using the cumulative average method, as previously described (Karacan
      et al). The positive peaks of the rectified EMG data were used as a trigger to average the
      accelerometer data and the rectified EMG data. The point on the cumulative average trace of
      the platform accelerometer data where the standard error (SE) was the lowest was considered
      the stimulus onset point. The point on the cumulative average trace of the rectified EMG data
      where the SE was lowest was considered the point of onset for the EMG spike. The mean height
      of young adult males in country (175 cm) was used to normalize of the T-reflex and WBV-IMR
      latencies (Cidem et al).

      2.5. Precautions for voluntary muscle contractions and motion artifacts Five measures were
      taken: 1) the participants were asked to use the handles of the WBV device to secure their
      balance. The sense of balance may impair during WBV. Therefore muscles may be activated to
      restore balance during WBV, 2) Before WBV trials, participants were asked to relax and not to
      make voluntary contractions in their lower extremity muscles. This instruction was provided
      with verbal feedback given by the researcher who monitored the SEMG recordings from the
      screen. If the RMS amplitude of EMG was lower than five microvolts during this intruction, it
      was accepted that muscle relaxation was accomplished by participant, 3) a trial protocol was
      applied to familiarize vibration, 4) all cables were carefully taped to the skin to minimize
      motion artifacts, 5) all EMG recordings were filtered to avoid WBV induced movement artifacts
      (Sebik et al., 2013).

      2.6. Statistical analysis The normal distribution of the data was confirmed using the
      Kolmogorov-Smirnov test. Continuous variables were summarized as arithmetic mean and standard
      deviation (SD).

      The paired sample t-test was used to analyze the statistical difference in the amplitude of
      WBV-IMR between weak and moderate WBV. General linear model repeated measures test was used
      to compare in the T-reflex latencies, WBV-IMR latencies or PPmax amplitude of T-reflex among
      the sessions. The alpha (α) threshold was chosen as 0.05. The Bonferroni test was applied for
      pair-wise comparisons (PostHoc analyses). Using a Bonferroni (a significance level for each
      pair-wise comparisons is α/m, m is the number of pair-wise comparisons), results with a p
      value ≤ 0.017 were considered significant. Confidence interval (CI), mean, and standard error
      (SE) were calculated for all data. When comparing means of two data sets, if ±95% CI of one
      data set included the mean of another data set, it was established that there is no
      statistical difference between the means of two data sets. The data management software
      package used was PASW statistics (formerly SPSS Statistics) for Windows.
    

Intervention name(s): vibration
Intervention type(s): Other
Intervention description(s): Whole body vibration
Other intervention name(s): Whole body vibration
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Whole body vibration; Tonic vibration reflex; Bone myoregulation reflex