Article Title



Zachary K. Pope & Jason M. DeFreitas

Oklahoma State University, Stillwater, Oklahoma

The physiological response to muscle vibration is complex. The repetitive length changes imposed by the mechanical oscillations strongly modulates proprioceptive activity, particularly the activity of the muscle spindles. Accordingly, vibration may represent a useful research tool to manipulate the sensitivity of the muscle spindle reflex arc. However, to truly understand its’ usefulness as a tool, the complex relationship between vibration dosage and spindle responsiveness requires a better understanding. PURPOSE: Thus, the purpose of this investigation was to examine the effects of acute and prolonged vibration on muscle spindle function. METHODS: A cross-over study design was utilized to determine the effects of vibration dosage on the patellar tendon reflexes of 20 volunteers (age 24.5 ± 4.6 years). A series of tendon taps were delivered using a custom reflex apparatus, during which surface electromyography, torque, and accelerometry signals were obtained. These signals were used to quantify reflex magnitude and latency for each of the following conditions: 1.) control, 2.) acute (i.e. 1-5 seconds) vibration and, 3.) prolonged (i.e. 20 minutes) vibration. The vibratory stimulus was applied perpendicularly to the distal quadriceps, just superior of the patella, using a percussion hammer set at a frequency of 66 Hz and was removed just prior to the reflex testing. RESULTS: When compared to the control condition, the results of the current study revealed that acute vibration did not significantly increase reflex torque magnitude (p = 0.461), but did significantly increase reflex latency (p = 0.022). Prolonged vibration, however, resulted in a significant depression of reflex magnitude (p = 0.001) and an increased reflex latency (p = 0.0002). CONCLUSIONS: The findings of the current study support the use of prolonged vibration as a means to suppress the muscle spindle reflex arc and lends credence to the contention of a peripheral origin for the altered motor response following prolonged vibration. The findings, in regards to the acute vibration condition, are less clear. It is speculated that the divergent responses for reflex magnitude and latency may indicate an altered composition of, or response to, the composite excitatory post-synaptic potential generated by the tendon tap.

This research was made possible in total or in part by funding through the award for the project number HR-14-023, from the Oklahoma Center for the Advancement of Science and Technology.

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