A Simple Method to Determine the Reflex Latency During WBV
Condition: Latency Period (Psychology)
Study type: Interventional

Summary: 
      The purpose of this study was to examine the validity of the measurement method based on
      observation of vibration stimulation-MUAP (motor unit action potential) (1 to 1) matching
      that helps to measure human WBV-induced muscular reflex latency and to compare these results
      with the latency determination obtained using the classical methods. The investigators'
      principle hypothesis is that the simple method is capable of determining the WBV induced
      reflex response latency as reliably as the complex methods described earlier.

      To achieve this goal, the investigators have averaged the electrical responses of the soleus
      muscle (sEMG and multi motor unit (MMU) potential) against the vertical force data obtained
      during all the six vibration frequencies tested in this study. The investigators have then
      combined all the averaged EMG data belonging to six different vibration frequencies to
      generate the 'cumulative averaged' sEMG and MMU for each subject. The investigators have also
      obtained the standard error for the cumulative averaged records which indicated the
      WBV-induced muscular reflex (WBV-IMR) latency.
    

Detailed description: 
      Subjects Five healthy volunteers will be participated in the study.

      Procedures During WBV, the subjects will be asked to stand upright on a vibration platform
      (PowerPlate Pro5, London, United Kingdom). Their hips and knees will be in a neutral
      position. Subjects will be barefooted, and no sponge or foam will be placed between the
      vibration platform and their feet (Figure 1). The whole plate oscillates with a linear
      movement upward and downward. Vibration amplitude is 2.2 mm. WBV frequencies will be varied
      randomly to cover the following six frequencies: 25, 30, 35, 40,45 and 50 Hz. Each frequency
      lasts for 60 seconds and there will be a 15 seconds rest in between different frequencies.

      A load sensor (FC2331-0000-2000L Compression Load Sensor, France) will be fixed on the WBV
      platform in order to be able to determine induced muscular response latency. Subjects will be
      positioned on the WBV platform such that their right heel will be placed on the load sensor.

      Recordings MMUs, surface EMG (sEMG) and force recordings will be simultaneously done using
      the Powerlab data acquisition system (ADInstruments, Oxford, United Kingdom). A sampling
      frequency of 40 kiloHertz (kHz) will be used. Data will be analyzed offline using the MATLAB
      (R2012a 7.14.0.739).

      In order to record sEMG, Ag/AgCl electrodes [KENDALL ® Arbo] with a disc radius of 10 mm will
      be placed 20 mm apart on the right soleus muscle belly, on shaved skin cleaned with alcohol.
      The ground electrode will be placed on the lateral malleolus.

      To record MMU activity, a pair of Teflon® insulated silver wires (75 µm in core diameter)
      will be used. About 3 mm of the tips of the silver wires will be stripped of their Teflon ®
      coating in order to be able to record the activity of several motor units. The pair of wires
      will be inserted into the right soleus muscle with a 25 G needle. Needle will be immediately
      withdrawn leaving the fish-hooked wires in the muscle. A lip-clip electrode will be used as
      the ground electrode.

      All cables will be carefully taped to the skin to minimize mechanical artifacts.

      The subjects will be instructed to relax their muscles throughout the recordings and were
      trained using EMG feedback to this end. WBV may impair the sense of balance and muscles may
      be activated to restore balance. To overcome this issue, the subjects will be familiarized
      with WBV with a 15 s session of WBV, the subjects will be asked to use the handles of the WBV
      device to secure their balance and the base of support (distance between the heels) will be
      adjusted as wide. The distance between the heels usually will be about 25 cm.

      Filtering and Rectification regimens All force sensor recordings will be 5 Hz high-pass
      filtered. All sEMG recordings will be 80 - 500 Hz band-pass filtered (Butterworth 1st order)
      and full-wave rectified to overcome movement artifacts. All MMU recordings will be 100-5000
      Hz band-pass filtered (Butterworth 1st order) and full-wave rectified.

      WBV - induced muscular reflex (WBV-IMR) latency

      In a previous study, right soleus muscle sEMG measurement and force sensor measurement that
      is placed under right heel during WBV were taken synchronously and it was found that
      vibration stimulation and MUAPs would be matched 1 to 1. In this study that is based on the
      previous observation, it is predicted that it is possible to calculate latency by using
      averaging method.

      All MMU and sEMG data will be analyzed by applying respectively filtering, rectification and
      differentiation with MATLAB (R2012a 7.14.0.739). Data analysis will be performed in two
      stages:

        1. Detection of the moment of mechanical stimulation threshold (Force Sensor Data
           Averaging): Force sensor data will be averaged by using Spike triggered averaging (STA)
           method. For this, 50 seconds of constant time intervals of preset vibration frequency in
           a WBV set will be used. All the positive peaks in both MMU and sEMG traces will be
           marked. For all the positive peaks, the force sensor trace will be segmented covering 75
           ms previous positive peak. After, cumulative average of these 6 vibration sets will be
           averaged. The standard error on the cumulative averaged force records will be
           calculated. The lowest point of standard error on force sensor averaging graphic will be
           considered as the starting point of mechanical stimulation that triggers the muscle
           response.

        2. Determination of the MUAP onset: EMG data averaging method and manual method (vibration
           stimulus and MUAP coupling) will be used.
    

Intervention name(s): whole-body vibration
Intervention type(s): Other
Intervention description(s): High amplitude whole-body vibration
Other intervention name(s): Cyclic mechanical loading
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: muscle electrical activity; whole-body vibration; latency