High-Frequency Whole Body Vibration Activates Tonic Vibration Reflex

Seven healthy recreationally active males between the ages of 26 and 35 volunteered to participate in this study. All subjects received pre-study informed consent. All experimental procedures were designed with the Helsinki declaration in mind and approved by the local ethics committee. All subjects performed a familiarization trial to acclimate subjects to the WBV stimulus. WBV-IR and TVR latency of soleus muscle were then measured in the quiet standing position. The vibrations (WBV or tendon) sequence were applied randomly to negate any order/time effect. The subject rested for five minutes between the WBV and tendon vibration. The WBV application was delivered using a PowerPlate Pro5 device (PowerPlate International, Amsterdam, The Netherlands). First, 30 Hz, low amplitude (1 mm) vibration with a duration of 30 seconds was applied to each subject for familiarization purposes. After three minutes of rest, low-amplitude (1 mm) WBV testing was performed in random order in quiet standing positions. In a WBV set, three different vibration frequencies (30, 35, and 40 Hz), each lasting for 30 s with 3-s rest intervals, were delivered. The local vibration was applied to the mid-point of the right Achilles tendon by using a custom-made vibrator. The head of the tendon vibrator was in light contact with the underlying skin. Tendon vibrations were applied by the same researcher. Three different vibration frequencies (100, 135, and 150 Hz) were delivered, lasting for 30 s with 3-s rest intervals. A local vibration was applied to the right heel using the same custom-made vibrator. Tendon vibrations were applied by the same researcher. Three different vibration frequencies (100, 135, and 150 Hz) were delivered, lasting for 30 s with 3-s rest intervals.

The surface electromyography (SEMG) recorded from the soleus and acceleration data were collected simultaneously using data acquisition and analysis system (PowerLab ® software, ADInstruments, Oxford, UK). Disposable self-adhesive bipolar Ag/AgCl (Covidien Kendall, Dublin, Ireland) surface electrodes were placed on the right soleus belly 4 cm apart. The skin overlying the muscle was shaved, light abrasion was applied, and the skin was cleaned with alcohol to reduce the skin resistance. To determine TVR latency, a light (2.9 g) piezoelectric accelerometer (LIS344ALH, ECOPACK®, Mansfield, TX, USA) was firmly fixed using adhesive tape on the skin overlying the right Achilles tendon. To determine WBV-IR latency, an identical accelerometer was firmly mounted on the WBV platform. The acceleration and SEMG signals were recorded at a sampling frequency of 20 kHz. Accelerometer recordings were filtered with a high-pass filter set at 5 Hz. SEMG data obtained during WBV were bandpass filtered at 80-500 Hz to reduce vibration-induced movement artifacts and then full-wave rectified. Similarly, SEMG data obtained during tendon vibration were bandpass filtered at 160-500 Hz and then full-wave rectified. WBV-IR and TVR latencies were then calculated by using the cumulative average method.

An electronic reflex hammer (Elcon, Germany) was used to determine T-reflex latency. All latencies were normalized to the body height of each participant.

Latency was expressed as milliseconds (ms).