Unit 3 DP 1

⚡ NMES: Purpose and Indications

NMES = Neuromuscular Electrical Stimulation

Used to induce skeletal muscle contraction for:

Muscle strengthening

Prevention of disuse atrophy

Reduction of spasm/spasticity

Edema reduction

Improvement of range of motion

🔍 Motor Unit Recruitment: Physiological vs. NMES

Feature Voluntary Contraction NMES-Induced Contraction

Recruitment order Small (slow-twitch) → large (fast-twitch) Non-selective (small & large together)

Pattern Asynchronous Synchronous (fixed spatially & temporally)

Fatigue Slower onset Faster fatigue due to synchronous firing

Control CNS-driven Externally driven by electrode placement

Clinical Significance:

NMES can bypass CNS control to recruit muscle fibers, including deep fibers, improving strength even with neuromuscular deficits

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⚙ Types of Current

1. Russian Current

Type: Burst-Modulated Alternating Current (BMAC)

Carrier Frequency: 2500 Hz

Burst Frequency: 50 Hz

Duty Cycle Example: 10 sec ON / 50 sec OFF (≈ 20%)

Effect: Produces strong, tetanic muscle contractions

2. Pulsed Current

Type: Low-frequency (1–1000 Hz)

Control Parameters: Pulse duration & frequency

Used for: NMES on smaller muscles or when precise control is needed

💥 Frequency and Muscle Response

Frequency Response Notes

< 10 Hz Unfused twitches Muscle relaxes between pulses

30 Hz Fused contraction begins Smooth contraction

50 Hz Tetanic plateau Ideal for strength without excessive fatigue

> 100 Hz Fatigue risk Not recommended for sustained training

💪 Mechanisms of Strengthening

1. Muscle Mass Effects (Long-term):

Increase in muscle fiber cross-sectional area (weeks to months)

2. Neural (Non-Muscle) Effects (Short-term):

↑ number of recruited motor units

↑ firing frequency

↑ synchronization of recruitment

NMES Benefits:

Early gains due to neural adaptation, long-term gains from hypertrophy

📊 Common NMES Parameters for Strengthening

Parameter Typical Range / Recommendation

Pulse duration 200–350 µs (up to 400 µs)

Frequency 30–50 Hz (smooth tetany)

Intensity ≥50% of MVC or max tolerated

Ramp up/down ~2 sec (comfortable transition)

Duty cycle 10s ON / 30–50s OFF

Treatment time 10–20 contractions per session

Sessions 3–5 times/week for several weeks

Tip: Higher amplitudes and longer durations yield stronger contractions but must remain tolerable to the patient

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🧩 Parameter Considerations

To avoid fatigue:

Lower frequency (≈30 Hz)

Longer rest (off-time)

Ramp time: 1–2 sec preferred

Intensity: 50–70% MVC of contralateral limb (common in research)

High frequency (≥100 Hz): Faster fatigue, not ideal for strengthening

🩻 Motor Recruitment Evidence (MRI Study)

Even with superficial electrodes, NMES activates deep muscle fibers:

At 25% MVC → noticeable activation

At 50–75% MVC → deep and widespread activation

→ Supports effectiveness for large muscle groups like the quadriceps

⚙ Electrical Stimulation for Denervated Muscle

Term: “Electrical Stimulation (ES)” (not NMES)

Mechanism: Directly depolarizes the sarcolemma (no motor nerve input)

Parameters:

Pulse duration: ≥10 ms (very long)

Amplitude: High

Waveform: Direct current (DC)

Risk: Skin burns from prolonged DC exposure

Chronaxie comparison:

Innervated muscle: 0.2 ms

Denervated muscle: ~10 ms (much longer)

📍 Electrode Placement Examples

Muscle Placement Tip

Quadriceps Large pads; may require 4 electrodes for large patients

Posterior Rotator Cuff Aim to move humeral head superiorly in glenoid (avoid abduction)

Tibialis Anterior Adjust placement until balanced dorsiflexion achieved

Peroneals For foot drop correction; placement may vary

🚫 Contraindications

Do NOT place electrodes over:

Trunk/heart (pacemaker or ICD)

Pelvic/abdominal region (pregnancy)

Carotid bodies

Phrenic nerve or bladder stimulator

Areas of PVD, active osteomyelitis, hemorrhage, or gonads

⚠ Precautions

Use with caution in patients:

Without intact sensation or unable to communicate

With cardiac dysfunction (arrhythmias, uncontrolled BP)

With epilepsy or cognitive impairment

Over or near neoplasms, compromised skin, or cervical regions post-CVA

Avoid use near diathermy units due to electromagnetic interference