Vibration for stimulating limb proprioceptors: Measurement, characteristics, and challenges


Using tendon/muscle vibration to stimulate Ia afferents in rehabilitation research is increasing in popularity. Tendon vibration can also be used to stimulate the mechanoreceptors with the goal of attenuating proprioception. For therapeutic purposes, tendon vibration must be within known amplitude(~0.5mm) and frequency(80-120Hz) ranges. However, there is no standard and portable method established for measuring vibration characteristics. The aim of the current study was to describe the characteristics of the movements of a vibration motor and explore the feasibility of using an affordable accelerometer to measure vibration characteristics. Movements of a small vibration motor mounted on a participant's wrist were simultaneously measured using an Optotrak 3D Investigator and accelerometer. Five vibration intensities (55%,65%,75%,85%,100% of motor capacity) were measured for five 30-second trials each. The main outcome measures were frequency, displacement and peak acceleration of the vibration from the Optotrak and accelerometer. Pearson correlations showed a strong positive relationship between accelerometer and Optotrak measurements of vibration frequency for 55%,65%,75%,85%, and 100% vibration intensities (r=0.86,0.99,1.00,1.00,1.00, respectively). The maximum acceleration of the motor's movement ranged from ±42.5m.s^2 to ±149.0m.s^2 for different vibration intensities as measured by the Optotrak. This range of acceleration is above the measurement range of the accelerometer used (range ±3g). Thus, the measurements of the accelerometer for vibration amplitude could not be validated. The results of this study showed that affordable accelerometers are capable of measuring the frequency of the vibration with high precision. A follow-up study will explore the validity of vibration amplitude measurement using an accelerometer with a measurement range of ~±10g.