NEUROMUSCULAR ELECTRICAL STIMULATION (NMES) - 20 Marks Answer

Definition and Introduction

1. Electrical Stimulation for Muscle Strengthening

Mechanisms of Strength Gain

• Spinal motor pool activation
• Synaptic facilitation
• Changes in muscle motor unit firing patterns (conversion from slow-oxidative to fast-oxidative glycolytic or fast-glycolytic units)

Waveforms for Strengthening

• Biphasic waveforms are the most effective for NMES.
• Evidence from Kramer et al. (1984), Walmsley et al. (1984), and Snyder-Mackler et al. (1989) supports asymmetric biphasic over symmetric biphasic waveforms for maximal quadriceps force production.
• There is an approximately linear relationship between current intensity and force of contraction (Ferguson et al., 1989; Underwood et al., 1990).
• Greatest effects with least current intensity are achieved using biphasic pulsed or burst AC currents.
• 2500 Hz burst AC (carrier frequency modulated) and symmetric/asymmetric biphasic pulsed currents are both widely used.
• Pulse widths of 300-400 microseconds may be optimal.

Stimulation Parameters for Strengthening

Stimulation Frequency and Force Generation

• Stimulation frequency directly affects force generation.
• Tetanic contractions (60-100 Hz) produce maximum force but also greater discomfort, potential muscle damage, and rapid fatigue.
• 20 Hz achieves approximately 65% of maximum force with significantly less fatigue - preferred in rehabilitation settings.

Electrode Placement

• Best results when both electrodes are placed on the muscle belly.
• One electrode should be at or near the motor point.
• Larger electrodes are preferable - they reduce current density and therefore reduce discomfort.
• Longitudinal orientation of electrodes produces stronger contraction with less discomfort (Brooks et al., 1990).
• Specialist electrodes are available for pelvic floor stimulation, and glove/sock electrodes are used for peripheral applications.

Strengthening Protocols

• 2500 Hz burst AC; symmetric or asymmetric biphasic pulsed current
• Frequency ~60 Hz, intensity at maximum tolerance; can achieve effects at 25-50% MVC isometric
• Duty cycle: 1:8-1:5 (fatigue-prone); 1:3-1:2-1:1 (fatigue-resistant)
• 8-15 max contractions/session; 3-5 sessions/week; 3-6 weeks for significant effect

• Lower frequencies (20-35 Hz, minimum to achieve tetany)
• Longer sessions; duty cycle to minimize fatigue (at least 1:4 or more)
• 100-200 contractions/session over 1-2 hours

2. Suggested Clinical Treatment Parameters

3. NMES for Range of Motion (ROM)

Effects on Passive ROM

• Munsat and coworkers reported that NMES of quadriceps for 6 hours daily was effective in reducing knee flexion contractures in 4 of 5 comatose patients (following surgical hamstring lengthening).
• Workers at Rancho Los Amigos Medical Center (1979) applied NMES to wrist and finger extensors in 16 hemiplegic patients with flexion contractures. Treatment began at 15 min twice daily, progressing to 3 sessions/day, 7 days/week for 4 weeks at maximum comfortable extensor contraction through full available ROM.
• When NMES was discontinued in four patients, passive extension gradually declined, highlighting the need for continued exercise.

Effects on Active ROM

• Bowman and coworkers reported on effectiveness of NMES for active ROM restriction in 30 hemiplegic patients who had full passive ROM but limited active ROM (5-30 degrees).
• Subjects received conventional therapy plus NMES: 30 min, twice daily, 5 days/week for 4 weeks.
• The stimulated group improved active wrist extension by 35%, compared to only 8% in the control group.

4. NMES for Spasticity Control

Three Approaches:

• Duchene (1871) first reported on electrical activation of antagonists to spastic muscles.
• Levine and coworkers (1950s) used uninterrupted faradic currents at 100 pps using monopolar electrode over motor point of antagonist muscle, at amplitude sufficient for maximum contraction.
• Reported relaxation of hypertonicity within seconds; reduction in spasticity with improvements in self-care, mobility, and posture.
• Baker and coworkers (late 1970s): NMES to wrist/finger extensors in 16 hemiplegic patients with flexor spasticity. Rectangular monophasic pulses, 200 µs pulse duration, 33 pps, 7 sec ON/10 sec OFF, bipolar setup. Duration: 15 min twice daily, increasing to 30 min three times/day for 4 weeks.
• Reduction in wrist flexor spasticity persisting approximately 30 minutes after stimulation.

• Lee and coworkers studied this approach in 27 spinal cord injury patients.
• Bipolar electrode; continuous faradic or sinusoidal stimulation at 60-100 pps (faradic) or 60-350 Hz (sinusoidal).
• Stimulation intensity set to maintain maximum contraction; in some cases increased and decreased to elicit alternating contraction and relaxation.

• Vodovnik and coworkers (early 1980s) alternately activated spastic and antagonist muscles in 7 spinal cord injury patients.
• Asymmetric biphasic pulses at 30 pps, pulse duration 300 µs, amplitude 100 mA; 5 sec ON / 5 sec OFF.
• Results did not show reciprocal pattern to be superior to either agonist or antagonist stimulation alone.

5. Conclusions on NMES and Strengthening

• NMES consistently produces strength increases compared to unexercised controls.
• No significant difference generally exists between NMES and voluntary exercise with similar regimens - both show significant gains over controls.
• No added benefit from simultaneous NMES plus voluntary exercise over either alone.
• Electrically elicited quadriceps contractions in the range of 80-100% of MVIT are possible.
• Certain muscle stimulation regimens produce greater strength gains than voluntary exercise in patient populations.
• A positive correlation exists between training contraction intensity and strength gains in people with muscle weakness.
• A positive correlation exists between phase charge and torque-generating capability in patients.
• Electrical stimulation has strengthening benefits even at lower training contraction intensities.

6. Precautions and Contraindications for NMES (Thoracic Region)

• Cardiac pacemakers
• Phrenic nerve or urinary bladder stimulators
• Carotid sinus stimulation
• Hypertensive or hypotensive patients
• Peripheral vascular disease
• Neoplasm or active infection
• Obese patients

7. Application Principles for NMES

1. Firm and proper stabilization of the body part must be provided.
2. Stimulation parameters are selected appropriately.
3. Electrodes secured and subject stabilized.
4. Initial session: amplitude is gradually increased until motor threshold is reached and exceeded.
5. In the first session, amplitude may need to be increased contraction by contraction to gradually build subject tolerance and contraction force.
6. A 5-7 day programme of stimulation is the standard initial approach; contraction period less than 10 sec with rest period of 10-20 sec.

8. Clinical and Research Applications

• Musculoskeletal/Orthopaedic: Quadriceps strengthening post bilateral total knee arthroplasty (Stevens et al., 2004); patellofemoral pain (Callaghan & Oldham, 2004); quadriceps torque comparison between clinical and portable stimulators (Lyons et al., 2005).
• Cardiovascular: Chronic low-frequency thigh muscle stimulation in advanced chronic heart failure (Nuhr et al., 2004); NMES for muscle weakness in advanced disease (Maddocks et al., 2013 - Cochrane Review).
• Neurological - Stroke: Shoulder pain/dysfunction in hemiplegia (Chantraine et al., 1999); prevention of shoulder subluxation post-stroke meta-analysis (Ada & Foongchomcheay, 2002); quadriceps motor unit recruitment after stroke (Newsam & Baker, 2004).
• Neurological - Spinal Cord Injury: Skeletal muscle adaptability after SCI with ES leg training (Crameri et al., 2002); acute phase ES training (Crameri et al., 2000); clinical applications post-SCI (Creasey et al., 2004); switching stimulation patterns to improve paralyzed quadriceps (Scott et al., 2005); ES in SCI rehabilitation (Sadowsky, 2001).

INSTRUMENTATION OF NMES - 10 Marks Answer

Introduction

1. Current Waveform Selection for NMES

Subject Comfort

Force of Contraction

• Amplitude
• Pulse duration
• Frequency
• Waveform shape

• Symmetrical biphasic waveforms and burst-modulated sinusoidal AC waveforms may be most appropriate for electrical activation of normally innervated skeletal muscle.
• Very short duration monophasic waveforms may be slightly less effective than symmetrical biphasic waveforms for force generation.

2. Recommended Stimulator Features and Controls

1. Two output channels - allows simultaneous stimulation of two muscle groups or bipolar placement.
2. Pulse/phase duration controls - to adjust stimulus duration for comfort and efficacy.
3. Frequency controls - to select appropriate stimulation frequency for the clinical goal.
4. Independent amplitude controls - separate intensity control for each channel.
5. ON time / OFF time controls - to set the duty cycle (contraction and rest periods).
6. Ramp modulation control - for gradual rise and fall of stimulation intensity.
7. Timer - for session duration monitoring.

3. Portable vs. Clinical Stimulators

• May not provide sufficient output to bring skeletal muscle contractions to therapeutic levels.
• At high output levels, battery power is drained quickly, requiring frequent battery replacement.
• Generally lack analog or digital outputs, limiting their monitoring capability.

4. Electrodes and Electrode Placement

Placement Sites

• At the muscle belly - preferred for optimal muscle activation.
• At the motor point - the location of lowest resistance to stimulation; produces strongest contraction with lowest current intensity.
• Bipolar electrode placement - both electrodes placed over the target muscle belly.

Types of Electrodes

1. Metal electrodes
2. Carbon-impregnated silicone rubber electrodes - commonly used, flexible, reusable.
3. Solvent-activated silver-impregnated tape electrodes
4. Self-adhering pre-gelled electrodes - most commonly used in clinical practice today for ease of application and consistent contact.

5. General Application Principles for NMES

1. Goal: To achieve high levels of stimulated muscle contraction.
2. Initial amplitude setting: As treatment begins, amplitude is gradually increased until the motor threshold is reached and then exceeded to elicit a visible/palpable contraction.
3. First session progression: Amplitude may need to be increased contraction by contraction in the first session to gradually increase subject tolerance and build contraction force.
4. Session monitoring: The stimulator's timer and duty cycle controls ensure appropriate work-to-rest ratios are maintained throughout the session.
5. User responsibility: Since stimulators offer considerable parameter flexibility, the clinician must understand the physiological consequence of each parameter adjustment to maintain safety and effectiveness.

1. How NMES works (mechanism step-by-step)
2. Electrode selection & placement decision flow
3. Strengthening protocol selection (patient type)
4. Three approaches to spasticity management
5. Step-by-step clinical NMES application
6. Electrode placement for optimal NMES (instrumentation)

🧠 TOPIC 1: NMES (Neuromuscular Electrical Stimulation)

WHAT IS NMES? (The 1-Line Answer)

NMES = Using electricity to make a nerve fire, which then makes a muscle contract.

WHY DO WE USE IT? (4 Big Goals)

1. S - Strengthen weak muscles
2. R - Improve Range of Motion (passive + active)
3. S - Reduce Spasticity
4. C - Cardiovascular/neurological rehab (SCI, stroke, heart failure)

PART 1: NMES FOR STRENGTHENING

How does NMES make muscles stronger?

• Activates the spinal motor pool (more motor neurons fire)
• Synaptic facilitation (connections in the spinal cord get better)
• Changes muscle fiber type (slow fibers convert to faster ones)

Easy memory: "NMES teaches the nervous system to work better, not just the muscle."

Key Research Facts (Write these in exams!)

Crossover Effect (Easy to Remember)

You stimulate the right quad, and the left quad also gets a bit stronger (10%). This happens because the spinal cord is shared!

THE 5 PARAMETERS - "FPDDR"

• F = Frequency
• P = Pulse width
• D = Duty cycle
• D = Duration of session
• R = Ramp

1. FREQUENCY (Hz) - "How many pulses per second?"

Memory trick: Higher Hz = More force BUT more fatigue. Like running fast - you get tired quickly.

2. PULSE WIDTH - "How long is each pulse?"

• 300-400 microseconds is the sweet spot for NMES
• Wider = more uncomfortable
• 400 µs is used across most clinical protocols

Memory trick: Think of it as how long you press a doorbell. Too short = nothing happens. Too long = annoying.

3. DUTY CYCLE (ON:OFF ratio) - "Work vs. Rest"

Memory trick: "Weaker patient = MORE rest. Like a new gym member who needs long breaks between sets."

Progress direction: Start at 1:9 → work toward 1:1 as patient gets stronger.

4. RAMP - "The gentle start and stop"

• Ramp UP: Gradually increase intensity at the START (2-4 seconds)
• Ramp DOWN: Gradually decrease at the END (1-2 seconds)

Memory trick: Like a car - don't floor the accelerator from zero. Ease in, ease out. Up is longer (2-4s), down is shorter (1-2s).

5. WAVEFORMS - "Which current shape is best?"

Winner: Asymmetric Biphasic Pulsed current (best force for quadriceps) Runner-up: Burst AC (2500 Hz)

Simple memory: "Asymmetric Biphasic Wins" - ABW

ELECTRODE PLACEMENT - "MOLL"

• Motor point = place where nerve enters muscle = least resistance = most contraction at least current
• Both electrodes on muscle belly when possible
• Longitudinal orientation = along the muscle fibers (stronger contraction, less discomfort)
• Larger electrodes = lower current density = less pain

STRENGTHENING PROTOCOLS TABLE

CONCLUSIONS (Exam gold - 5 easy points!)

1. NMES > unexercised control ✅
2. NMES = voluntary exercise (similar results when regimen is matched) ✅
3. NMES + voluntary = NO extra benefit over either alone ✅
4. Can achieve 80-100% MVIT with electrical stimulation ✅
5. Positive correlation: training intensity → strength gain ✅

NMES FOR ROM

Passive ROM

• NMES of quads, 6 hrs/day
• Reduced knee flexion contractures in comatose patients (after hamstring surgery)
• When NMES stopped → ROM declined again (important point!)

• 16 hemiplegic patients, wrist/finger flexion contractures
• NMES to wrist/finger extensors
• Started 15 min twice daily → progressed to 3x/day for 4 weeks
• Result: Improved passive extension

Active ROM

• 30 hemiplegic patients, full passive ROM but limited active ROM
• NMES group: 35% improvement in active wrist extension
• Control (conventional therapy): only 8% improvement

Memory: 35 vs 8 - NMES wins big!

NMES FOR SPASTICITY

Spasticity = Hyperactive stretch reflexes + reduced dexterity from CNS damage (stroke, SCI, MS)

3 Approaches (Remember: "A-D-C")

Baker's key parameters: Monophasic rectangular, 200 µs, 33 pps, 7s ON/10s OFF, bipolar

PRECAUTIONS & CONTRAINDICATIONS - "PCHPPON"

APPLICATION STEPS (Simple 5-step process)

1. Assess patient, check contraindications
2. Set parameters (freq, pulse width, duty cycle, ramp, waveform)
3. Place electrodes (motor point, bipolar, longitudinal)
4. Stabilize the body part
5. Increase amplitude gradually until motor threshold exceeded
   • In first session: increase contraction by contraction to build tolerance
   • Typical programme: 5-7 days; contractions <10 sec; rest 10-20 sec

🔧 TOPIC 2: INSTRUMENTATION OF NMES

WHAT IS INSTRUMENTATION? (The 1-Line Answer)

Instrumentation = The machine, waveform, controls, and electrodes used to deliver NMES.

5 BIG TOPICS IN INSTRUMENTATION - "CREEP"

1. CURRENT WAVEFORM SELECTION

For Comfort (Delitto & Rose study)

• Tested: Sinusoidal, Triangular, Rectangular (all symmetric biphasic)
• Used on normal subjects activating quadriceps
• Comfort measured on VAS
• Result: NO waveform was found to be most comfortable when torque was matched

Memory: "All three are equal - no winner for comfort"

For Force of Contraction

• Symmetric biphasic and burst-modulated sinusoidal AC = most appropriate for normally innervated skeletal muscle
• Short duration monophasic = slightly LESS effective than biphasic

2. RECOMMENDED STIMULATOR FEATURES

"A stimulator needs 7 controls" - remember: "2-PF-AOR-T"

Simple memory: "2 channels, 5 controls, 1 timer" = a complete NMES machine

3. PORTABLE vs. CLINICAL STIMULATORS

Memory trick: "Portable is convenient but limited. Clinical is powerful but you can't take it home."

Key exam point: Some portable units at high output drain battery quickly AND lack digital/analog outputs for monitoring.

4. ELECTRODE TYPES (Nelson et al. - 4 types)

5. ELECTRODE PLACEMENT RULES (Same as NMES section)

"MOLL" again - Motor point, One there, Longitudinal, Larger

• Both electrodes on muscle belly (bipolar)
• One at/near motor point
• Longitudinal orientation (along muscle)
• Larger size = less discomfort

6. GENERAL APPLICATION PRINCIPLES

1. Goal = HIGH level contraction (not just a mild twitch!)
2. Gradually increase amplitude → exceed motor threshold
3. First session = increase contraction by contraction to build tolerance
4. User must understand every parameter change and its consequence
5. Flexibility in controls = clinician's responsibility for safety

FINAL MASTER CHEAT SHEET

NMES Parameters at a Glance

Goal            Freq     PW      Duty Cycle      Duration
─────────────────────────────────────────────────────────
Strengthening   30-35Hz  400µs   10s ON/10s OFF  30 min/day
Endurance       20Hz     400µs   2s ON/2s OFF    1 hr/day
Very Weak       10Hz     400µs   2s ON/2s OFF    1 hr+/day
Athletes        ~60Hz    300-    1:8 → 1:1       8-15 contractions
                         400µs

The 3 Spasticity Approaches

• Antagonist → stimulate opposite muscle → 30 min relief
• Direct → stimulate spastic muscle → reduces hypertonicity
• Combined → no better than either alone

Key Numbers to Remember

• 35% vs 8% = active ROM improvement (NMES vs conventional)
• 24% + 10% = strength gains (Balogun - treated + crossover limb)
• 300-400 µs = best pulse width
• 2-4 sec ramp up / 1-2 sec ramp down
• 1:9 → 1:1 = duty cycle progression
• 8-15 contractions (athletes) vs 100-200 (rehab patients)
• 30 min post-stimulation = duration of spasticity relief (Baker et al.)
• 4 electrode types (Nelson et al.)
• 7 stimulator controls needed for NMES
• 2 output channels = basic requirement

Study tip: Read the cheat sheet 3 times tonight, cover it and write it from memory tomorrow morning. The numbers stick faster when you connect them to a clinical image - picture a post-knee surgery patient resting for 90 seconds between 10-second contractions, and the numbers will stay.

• Waveforms - ranked from best to least effective for force output
• Frequency scale - 10 Hz (atrophy) all the way up to 100 Hz (athletes)
• Duty cycle progression - visual 1:9 → 1:1 arrow showing how to progress patients
• Ramp - the rise-plateau-fall shape
• Clinical protocol table - 4 patient categories with exact settings
• Electrode placement rules
• Contraindications in a red warning box

• 🖼️ NMES poster = parameters, protocols, duty cycle, ramp, contraindications
• 🖼️ Instrumentation poster = waveforms, controls, electrodes, placement, application