Determination of Onset Point of Mechanical Stimulation

Overview

The difference between latencies of the tonic vibration reflex or T-reflex and whole body vibration-induced muscular reflex may be related to the distance between their stimulation point and the muscle spindles. Achilles tendon is mechanically stimulated by using a local vibrator to elicit the tonic vibration reflex or a reflex hammer to elicit the T-reflex. Whole body vibration, however, stimulates the soleus muscle indirectly over the heel, not directly, since whole body vibration is administered in a position that the subjects are standing on the whole body vibration platform. In other words, while the local vibrator or the hammer stimulates the Achilles tendon, whole body vibration stimulates the sole of the foot. During whole body vibration, mechanical vibration stimuli need to go a long way to reach the soleus muscle spindle. Therefore, whole body vibration-induced muscular reflex latency may be longer than tonic vibration reflex or T-reflex latency. The aim this study is to define a method for determination of onset point of mechanical stimulation inducing muscle spindle-based reflex (e.g., tonic vibration reflex, T-reflex) by using intramuscular electromyography electrodes.

The aim of this study is to define a method for the determination of the onset point of mechanical stimulation inducing muscle spindle-based reflex by using Intramuscular electromyography electrodes. This research protocol has two phases: First, the method of measuring latency using MAS was described in Experiment-I. The validity of this method was then determined in Experiment II. Eight healthy volunteers will participate in experiment-I and five healthy volunteers will participate in experiment II. Two surface electromyography electrodes will be placed on the left gastrocnemius muscle belly to record spindle-based reflex response. Single motor unit electrode pairs will be then inserted between two surface electrodes into the lateral gastrocnemius muscle to record stimulus artifact caused by tapping. The Achilles tendon will be tapped 20 times at 3-5 s intervals by a reflex hammer (Achilles tapping). Participants will be then asked to stand up and stand upright on the left foot. To maintain static balance, participants will be asked to hold the handles on the wall. The left heel will be tapped 20 times at 3-5 s intervals by a hammer (Heel tapping). In experiment II, the records from multiple sites gastrocnemius lateralis and rectus femoris) will be taken to characterize how movement artifacts change based on the location of the recording electrode. Using electric signals of the switch system as the trigger and the signals recorded by intramuscular electrodes and accelerometer as the source, spike-triggered averaging was used to determine the lag time it takes for the mechanical stimulus to reach the belly of the gastrocnemius and rectus femoris muscles. Meanwhile, the internal delay time of the accelerometers (the time between the mechanical stimulus moment and the signal output moment from the accelerometer) was determined. Using electric signals of the switch system as the trigger and the signals of accelerometers as the source, spike-triggered averaging was used to determine the internal delay time of accelerometers.