WK9: NMES & EMG Biofeedback

What is Neuromuscular Electrical Stimulation (NMES)?

The use of electrical currents to produce muscle contractions in innervated muscles (muscles with an intact nerve supply).

Which neurological system requirement must be intact for NMES to work effectively?

An intact, functioning Peripheral Nervous System (PNS)—including the motor nerve, neuromuscular junction, and muscle cells. (Central Nervous System injuries like stroke or spinal cord injury can still be treated with NMES as long as the PNS is intact).

Under what condition can NMES be used to treat edema (swelling)?

Only when the edema is caused by poor circulation due to lack of motion (lack of muscle pumping action).

Why is NMES contraindicated for swelling caused by acute inflammation, lymphedema, or organ failure?

Electrically induced muscle contractions can aggravate active inflammation and tear healing tissues; lymphedema and organ failure edema require systemic management and do not clear via a muscle pump.

How does muscle fiber recruitment order differ between a voluntary muscle contraction and an NMES-stimulated contraction?

Voluntary contractions recruit smaller nerve/muscle fibers first (orderly recruitment). NMES recruits larger nerve/muscle fibers first, producing higher force contractions that fatigue rapidly.

Why do NMES-induced muscle contractions fatigue much faster than natural, voluntary contractions?

Because NMES selectively activates large, fast-twitch muscle fibers first, which generate high force but lack endurance compared to slow-twitch fibers.

Why should patients perform voluntary contractions together with NMES contractions during strengthening exercises when possible?

Combining both optimizes recruitment of all muscle fibers (small fibers voluntarily, large fibers electrically) and promotes functional integration of strength gains.

What is Electrical Muscle Stimulation (EMS), and how does it differ from NMES?

EMS is electrical stimulation applied directly to denervated muscle cells (where the nerve is injured/severed), whereas NMES stimulates intact peripheral motor nerves.

What electrical stimulus parameters are required to trigger a contraction in a denervated muscle during EMS?

Direct Current (DC) or a pulsed current with a long pulse duration of 10 ms or longer.

What is Functional Electrical Stimulation (FES)?

Integrating NMES into functional, purposeful activities (such as walking, grasping objects, or standing) to assist movement patterns.

How is FES used to manage footdrop during gait training in patients with central nervous system disorders?

FES stimulates ankle dorsiflexors during the swing phase of walking to lift the foot and clear the toes.

Which nerve is targeted by FES electrodes to produce dorsiflexion and correct footdrop?

Deep fibular (peroneal) nerve.

Besides footdrop, what are two other clinical functional goals for FES application?

"1. Hand grasp/release (wrist flexor/extensor activation)

2. Spinal Cord Injury (SCI) conditioning, breathing assistance, standing, or bowel/bladder voiding."

How does the distance between two electrical stimulation electrodes affect current penetration depth?

Electrodes closer together yield a superficial current; electrodes further apart allow deeper current penetration into muscle tissue.

Why must electrical stimulation electrodes avoid direct placement over bony prominences?

Bone has very high electrical resistance, causing patient discomfort and poor current delivery to underlying muscle.

Where should electrodes be positioned over a target muscle to produce the strongest contraction?

Over the muscle's motor point (the location where nerve entry provides optimal excitability), running parallel to muscle fiber direction.

What asking points or diagnostic checks confirm that NMES is contraindicated due to tissue disruption risk?

Ask/check for: muscle or tendon tears, tendinitis/overuse injuries, or MD orders specifying no active motion or no resisted motion.

What are the two standard electrical waveforms used to produce muscle contractions in NMES?

Pulsed Biphasic waveform and Russian Protocol (burst modulated alternating current).

In the NMES waveform diagram below: NMES pulse amplitude versus time waveform showing distinct On time and Off time burst segments Why is an 'Off time' (duty cycle) necessary between muscle contraction periods?

The relaxation period (Off time) limits rapid muscle fatigue and allows recovery to maintain force production during subsequent contractions.

What is the recommended pulse frequency setting for NMES muscle strengthening?

35 to 80 pulses per second (pps).

How does recommended pulse duration for NMES differ between small and large muscle groups?

"Small muscles: 125–200 µs.

Large muscles: 200–350 µs."

What is the targeted contraction amplitude (% MVIC) for NMES strengthening of an injured or post-surgical muscle versus an uninjured muscle?

"Injured/post-op muscle: >10% of Maximum Voluntary Isometric Contraction (MVIC).

Uninjured muscle: >50% of MVIC."

What is the standard initial On:Off time and ratio for NMES muscle strengthening?

6–10 seconds ON, 50–120 seconds OFF (initial ratio of 1:5).

What is the minimum recommended ramp time for NMES muscle strengthening, and why is it used?

At least 2 seconds. Ramping gradually increases/decreases current for patient comfort and natural movement recruitment.

What is the standard treatment dosage (repetitions and session frequency) for NMES muscle strengthening?

10 to 20 repetitions (approx. 10–20 minutes per session), performed every 2–3 hours while awake.

What pulse frequency and ramp time settings are used for NMES muscle re-education during gait training?

"Frequency: 35–50 pps.

Ramp time: No ramp time (0 sec) when timed with gait phase."

What are the On:Off time ratio and ramp time requirements for NMES muscle spasm reduction?

"On:Off ratio: 1:1 equal ratio (2–5 sec ON, 2–5 sec OFF).

Ramp time: At least 1 sec (or 4–8 sec if stimulating the antagonist to a spastic muscle)."

What treatment parameters are used for NMES edema reduction via the muscle pump?

Frequency: 35–50 pps; Duration: 125–200 µs (small) or 200–350 µs (large); Amplitude: Visible contraction; On:Off: 2–5s ON / 2–5s OFF (1:1 ratio); Ramp: >=1s; Duration: 30 minutes twice daily.

What required elements must be included in NMES clinical documentation to ensure treatment reproducibility?

Body area treated, patient positioning, specific stimulation parameters (frequency, duration, duty cycle, ramp), electrode placement/size, treatment duration, and patient response.

What is Electromyographic (EMG) Biofeedback?

A diagnostic modality that measures, amplifies, and visually/audibly displays electrical activity (myoelectrical signals in µV) of underlying muscle to assist self-regulation.

Does an EMG biofeedback unit deliver electrical current to the patient's body?

No. EMG biofeedback only reads and records electrical activity produced by the body's own muscle contractions.

In EMG biofeedback readings, what do visual deviations (peaks and valleys) away from the isoelectric baseline signify?

The amount of muscle tissue electrically active during contraction or involuntary guarding.

What three electrode leads are used in a standard surface EMG biofeedback configuration?

Two active (sensing) electrodes and one reference (ground) electrode.

Where should active (sensing) electrodes and reference (ground) electrodes be placed for EMG biofeedback?

"Active electrodes: Directly over the target muscle belly, oriented parallel to muscle fibers.

Ground electrode: Over a non-contractile tissue or bony prominence."

How should EMG biofeedback machine gain (sensitivity) be set for an extremely weak muscle (e.g., peripheral nerve condition)?

Set to HIGH sensitivity / LOW gain (e.g., x1 gain on Myotrac) so even trace muscle activity triggers a visual/auditory feedback reward.

How should EMG biofeedback gain be set for a moderately weak muscle (e.g., post-op quadriceps with inhibition)?

Set to LOW sensitivity / HIGH gain (e.g., x10 or x100 gain) to require a strong, forceful contraction to reach the visual threshold.

How is EMG biofeedback gain set when training relaxation for an extremely tight or spastic muscle?

Set to LOW sensitivity / HIGH gain (e.g., x100 gain) so that even slight muscular relaxation registers on the screen.

What are the primary clinical contraindications and precautions for EMG biofeedback?

Acute inflammatory conditions (where active movement impairs healing) and pregnancy (avoiding intravaginal devices due to infection risk).

What proper skin preparation steps must be taken prior to applying biofeedback or NMES electrodes?

Trim excess hair, clean skin with alcohol or soap/water to remove oils, and let skin dry completely to lower skin resistance.

In the diagram below showing anterior thigh electrode placement: Anatomical thigh diagram highlighting two pairs of electrode placements marked A and B on the anterior leg Which muscle sites are represented by placement A and placement B?

"Placement A (upper thigh): Rectus Femoris.

Placement B (distal medial thigh): Vastus Medialis Oblique (VMO)."

In the lower leg diagram below: Anterior lower leg diagram displaying paired electrode placement over the upper lateral shin Which muscle is targeted by this electrode arrangement?

Tibialis Anterior.

In the forearm electrode layout shown below: Forearm diagram showing two electrodes arranged in line along the longitudinal orientation of the arm muscles Why are the electrodes aligned lengthwise along the forearm?

To direct current longitudinally along the direction of the target muscle fibers for effective motor unit recruitment.

Examine the ankle dorsiflexion response pictured below: Photograph of lower leg electrical stimulation resulting in toe clawing and hyper-extension of toes during foot lift What movement error is occurring, and which muscle is being unintentionally over-stimulated?

Unbalanced dorsiflexion response with excessive toe extension, caused by stimulating Extensor Digitorum Longus or Extensor Hallucis Longus instead of isolating Tibialis Anterior.

Examine the optimal ankle stimulation outcome pictured below: Photograph of lower leg electrical stimulation producing clean ankle dorsiflexion without toe extension What clinical term describes this desired movement response?

Balanced dorsiflexion response.

Refer to the anatomical diagram of the anterior leg: Anatomical diagram of lower leg depicting green highlighted Tibialis Anterior, red Extensor Digitorum Longus, and purple Extensor Hallucis Longus Which muscle must be targeted to achieve pure dorsiflexion without excessive toe extension?

Tibialis Anterior.

What post-treatment skin change is expected after NMES or biofeedback electrode removal?

Mild skin redness (erythema) under the electrode site is normal and should completely disappear within 24 hours.

What does the abbreviation MVIC stand for in NMES treatment protocols?

Maximum Voluntary Isometric Contraction (measured on the uninjured limb).