The EMG Signal

H-reflexes

H-reflex

Originally described by Piper in 1912 More clearly elucidated by Hoffman in

1922– Studied the gastrocnemius by electrically

stimulating the main trunk of the tibial nerve Magladery and McDougal (1950) credited

with designating the reflex response the Hoffman reflex – Shortened to the H-reflex

H-reflex Theory.1 The electrical equivalent of the deep tendon

reflex for testing a monosynaptic loop

Group Ia fiber

Spindle

Gross muscle

Reflex hammerAlpha motoneuron

Spinal cord

H-reflex Theory.2 The electrical equivalent of the deep tendon

reflex for testing a monosynaptic loop1

Group Ia fiber

Spindle

Gross muscle

Alpha motoneuron

Spinal cord

EMG

RecordingElectrodes

GalvanicStimulator

StimulatingElectrodes

1Hugon, 1971

H-reflex Theory.3

Confirms the integrity of the afferent - efferent nerve connections

Amplitudes (mV) provide an index of alpha motoneuron excitability at the spinal cord level

H-reflex Uses.1

First used as a clinical/diagnostic tool– Most frequently used to study the tibial nerve in

the posterior compartment of the thigh» Gastrocnemius usually studied

» Compare latencies between M-waves and H-reflex bilaterally

Correlates with leg length - range = 22.64 - 40.14 msec (tibial nerve)

H-reflex Uses.2

Examples - Clinical/Diagnostic Use– Assess the integrity of the S1-2 nerve roots with

suspected foraminal encroachment (Braddom & Johnson, 1974)

– Takamori (in Braddom & Johnson, 1974) studied patients with spasticity and Parkinson’s disease

– Magladery & McDougal (1950) studied nerve disorders secondary to ischemia

H-reflex Uses.3

More recently the H-reflex has been used in clinical and basic research

Tibial, common peroneal, femoral, median and ulnar nerves have been studied with varying degrees of success

H-reflex - Uses.4

Mongia (1972) studied the femoral nerve and quadriceps

Bulbulian & Bowles (1992) studied eccentric contractions in downhill running

Kennedy et al. (1982); Spencer et al. (1984); and McDonough & Weir (1996) studied reflex inhibition in the quadriceps secondary to knee joint capsular swelling

Neurophysiological Overview.1

After the nerve (e.g., femoral, tibial, etc.) has been identified and stimulating electrodes are applied over the nerve, and after recording EMG electrodes are applied over the muscle’s motor point…

A galvanic stimulator simulates the nerve (group Ia afferents) directly thereby by-passing the spindle

Neurophysiological Overview.2

Group Ia fibers monosynaptically connect with alpha motoneurons in the anterior horn of the spinal cord

The alpha motoneurons activate extrafusal (somatic) fibers in the homonymous muscle– Recording EMG electrodes pick-up electrical

activity in the muscle A twitch contraction is elicited

– Similar is appearance to a DTR response

EMG Response - Vastus Medialis

Stimulus artifact

M-wave H-reflex

Volts

Latency

msec

Potential Confounding Influences

Head/neck position Mental/emotional/alertness state Cognitive state Ambient temperature The specific nerve being studied Stimulating electrode conditions

Procedure.1 - Femoral Nerve

Using a galvanic stimulator with a probe electrode identify the motor points of VM and VL– Apply EMG electrodes in the standard way with

standard skin prep» Reference electrode over ASIS

– Confirm signal using Scope1.vi Palpate the femoral artery pulse in the femoral

triangle - mark the skin

Procedure.2 - Femoral Nerve

Using a galvanic stimulator with a probe electrode locate the femoral nerve 1-2 cm lateral to the femoral artery - mark skin– Confirm with Scope1.vi

Apply a pre-gelled, self-adhesive electrode over the femoral nerve– Large dispersal electrode on back of thigh

Procedure.3 - Femoral Nerve

Stimulator settings– Rate: 0.30 - 0.40 Hz– Duration: 0.50 - 1.0 msec– Intensity: 40 - 110 volts

Collect data using Bincolct.vi– Saves data in binary format

~10 seconds of rest between trials

Procedure.4 - Femoral Nerve

Using Scope1a.vi bring intensity (voltage) up gradually until an M-wave and H-reflex are visualized

Decrease intensity in ~5 volt increments until the M-wave decreases in amplitude but the H-reflex remains constant

Procedure.5 - Femoral Nerve

Run Bincolct.vi– Will continue to collect data until Stop button is

pushed– Every 10 seconds press stimulator switch “On”

to elicit H-reflexes

Bincolct.vi

Procedure.6 - Femoral Nerve

Analyze data using Hread.vi (reads binary format data)– Run the VI– Each time the SHOW NEXT button is pushed

1000 data points will be advanced– Approximately every 10 seconds a triplex of

signals will appear» Stimulus artifact

» M-wave

» H-reflex

Hread.vi

EMG Response - Vastus Medialis

Stimulus artifact

M-wave H-reflex

Volts

Latency

msec

Procedure.7 - Femoral Nerve

To “stretch-out” the triplex of waves adjust (re-scale) the ‘x-axis’ values

Measure waveform amplitudes (V; mV) and latencies (msec) using Cursor Display

References

Braddom, R.L., & Johnson, E.W. (1974) H-reflex: Review and classification with clinical uses. Archives of Physical Medicine and Rehabilitation, 55, 412

Enoka, R.M. (1994). Neuromechanical basis of kinesiology (2nd ed.). Champaign, IL: Human Kinetics, pp. 177-179.

Enoka, R.M., Hutton, R.S., & Eldred, E. (1980). Changes in excitability of tendon tap and Hoffman reflexes following voluntary contractions. Electroencephalography and Clinical Neurophysiology, 18, 664-672.

References

Garland, S., Gerilovsky, L, & Enoka, R.M. (1994). Association between muscle architecture and quadriceps femoris H-reflex. Muscle & Nerve, 17, 581-592.

Hugon, M. (1973). Methodology of the Hoffman reflex in man. In J.E. Desmedt (Ed.). New developments in electromyography and clinical neurophysiology. Basel: Karger, pp. 277-293.

Kennedy, J.C., Alexander, I.J., & Hayes, K.C. (1982). Nerve supply o f the human knee and its functional importance. The American Journal of Sports Medicine, 10, 187-194.

References

Magladery, J.W., & McDougal, D.B. (1950). Electrophysiological studies of nerve and reflex activity in normal man: Identification of certain reflexes in electromyogram and conduction velocity of peripheral nerves. Bulletin of Johns Hopkins Hospital, 86, 265-290.

McDonough, A.L., & Weir, J.P. (1996). The effect of post-surgical edema of the knee on reflex inhibition of the quadriceps femoris - a case study. Journal of Sport Rehabilitation, 5, 172-181.

References

Mongia, S.K. (1972). H-reflex from quadriceps and gastrocnemius muscle. Electromyography and Clinical Neurophysiology, 12, 179-190.

Spencer, J.D., Hayes, K.C., & Alexander, I.J. (1984). Knee joint effusion and quadricepsreflex inhibition in man. Archives of Physical Medicine and Rehabilitation, 65, 171-177.