From simple single ended to versatile multiparameter measurements
Note: Disconnect the subject from the IXTA prior to powering off the device.
Aim: To investigate the H-reflex response and the M-wave response during muscle stimulation.
Approximate Time: 60 minutes
Increase the current of the SI-200 to 2 mA (1.0 on the dial or using the IXTA Stimulator Control Panel).
Check the Setup file to determine the initial stimulator preferences.
When using the IXTA – click the “Apply” button to make any changes.
A 120 msec tracing will be displayed on your computer screen.
There should be 20 msec of inactivity followed by the 1 msec stimulus.
You will notice the artifact from the stimulus in your EMG channel. Approximately 30 msec later you will see the H-reflex appear if the stimulus was large enough and threshold was reached.
If nothing appears, confirm with the participant a stimulus was delivered and if the subject felt any tingling sensation.
If so, increase the current on the stimulator by 1 mA, then deliver the stimulus again.
Repeat steps 2-5 until an H-reflex is recorded so its peak to peak maximum is at its highest. To do this you will need to use the double cursor function A tracing example is shown below.
Repeat the procedure with a slightly increasing stimulus, no more than 1mA at a time. Stop at any time the subject does not wish to continue.
Note: If the trace is upside-down, click the Invert button using the down arrow to the left of the Soleus channel.
The maximal peak to peak EMG amplitude is considered the maximal H-reflex. Note that the tracing is very similar to that seen in a reflex hammer test of the Achilles tendon – see the Achilles Reflex Lab.
The value of the H-reflex is that the location of the stimulus and the intensity of the stimulus are easily controlled via bypassing the muscle spindle completely. Afferent neurons receive direct stimulation from the electric current provided by the stimulator.
The H-reflex is highly variable if the supraspinal input is not controlled. That is to say, any activity that causes the brain to function differently could lead to altered descending nerve tract information that could affect reflex activity. Interneurons synapsing with the descending tracts could facilitate or inhibit reflex output.
An example of this is the Jendrassik maneuver where you try to pull your hands apart during the reflex measurement. Changes in temperature, limb position, auditory input, visual input, stress, etc. can all affect maximal H-reflex amplitude.
In the main window, double the display time so that the recording resembles the trace shown above.
Click and drag the cursors so that the left hand cursor is on the stimulus and the right hand cursor is on the peak of the response. Measure T2-T1 for the time it took for the H-reflex to occur from the delivery of the stimulus.
With the right hand cursor still on the peak of the response, move the left hand cursor so that it is on the maximal downward spike of the H-reflex. Measure V2-V1 for the amplitude of the complete Hoffman Reflex of the soleus muscle.
Once the cursors are placed in the correct positions for determining the reflex conduction time and the amplitude of the reflex response, record the value for T2-T1, and V2-V1 in the Journal. The value can be recorded in the on-line notebook of LabScribe by typing its name and value directly into the Journal. Values can also be recorded in separate data table.
Try using the Jendrassik maneuver and determine the result on the Hoffman Reflex.
Add a small weight to the foot.
Alter the temperature, using either an ice pack or moist heat pack, and determine the H-reflex in both situations.
Try collecting a maximal M-wave. Calculate the Hmax:Mmax ratio which is the standard for reporting in sports medicine.
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