• Frequency is the number of pulses delivered per second (pps or *Hz)
• Frequency is adjusted to create desired physiologic responses based on the available electrophysiology research

* Hz = Hertz (cycles per second). Used to denote frequency when Alternating Current waveforms are used.

• The recommended frequency range for NMES protocols is 30 – 75 pps. This range facilitates an increased firing rate that results
  in a tetanic contraction of muscle.
• Increasing frequency does not increase muscle recruitment, it simply increases the rate of firing. Therefore, in protocols that have
  little rest time and longer durations of stimulation lower frequencies are selected to minimize electrical fatigue of muscle
  

Note: When using Alternating Current, frequency is noted as Hertz (Hz)

Considerations:

• Prepare/clean skin with alcohol swab
• Choose the correct size electrode…….e.g. larger electrodes for larger muscle groups
• Identifying when the electrode is spent! Typically the patient will complain of a biting or stinging sensation when the electrode is spent
  (this sensation is a result of increased resistance in the electrode)
• Be certain that the electrode is firmly fixated to the skin lack of good contact results in discomfort due to higher current density
  

• Enhance muscle recruitment
• Facilitation of weak inhibited Muscles
• Retard muscle atrophy
• Stimulate motor (re)learning
• Muscle strengthening
• Increase ROM
• Edema management
• Reduction of Muscle Spasm

During a normal muscle contraction, muscle fibers are recruited according to the ‘size principle’ (Henneman)

    - Small type I muscle fibers recruited first
    - Large Type II fibers recruited later when the effort increases

Recruitment patterns during electrical stimulation are reversed:

- Type II fibers are the first to contract
- Type I fibers contract only later when the pulse width and intensity are raised above a certain threshold

Result: Training effect that preferentially trains the type II fibers

1. Stimulation of an inhibited/weak muscle while having the patient simultaneously contract while the current is on (most common).
2. Stimulation of a weak or inhibited muscle during which time the patient simply experience the contraction (without volitional participation),
   followed by trying to reproduce the contraction during the off time.
3. Stimulation of an inhibited/weak muscle without combining volitional exercise (least common)
   

Option #1

• Moderate level muscle contraction sufficient to
  recruit inhibited or weak muscle.

Option #2

• Dose to a fair + to good muscle contraction
  (MMT Scale)

Ramping up/down of amplitude:

• 2 second ramp up: 2 sec ramp down
  

• 1:1 to 1:5 ratio or manual trigger switch
• Lower intensity contractions requires less rest time -- e.g. 10 on: 10 off
• Higher intensity contractions requires greater rest time -- e.g. 10 on: ≥30 off
• How much time is necessary to complete reps?
• Based on the treatment duration, is the total volume of ex and stimulation reasonable?

Example: 15 minute Rx: Quad set for 10 sec with stimulation - Rest 10 sec during off time = 3 quad set per minute x 15 = 45 quad sets

• Excellent Support in the literature for using NMES as an adjunct to volitional exercise for the treatment quadriceps strength impairments
• High Intensity NMES in combination with a volitional exercise program has been shown to be superior to volitional exercise alone after ACL reconstruction.1
  

1. Snyder-Mackler et al. J bone Joint Surg. 1995;77:1166-1173)

Problem of persistent quadriceps weakness s/p ACL reconstruction

• Wilk et al reported that only 7% of subjects at 6 months S/P ACL reconstruction achieved 90% of uninvolved quad strength on isokinetic
  testing at 180 deg/sec.
• Quad strength recovery 1 yr S/P ACL recon 61%- 91%.

Arangio,et al JOSPT 1997

Quadriceps Weakness S/P Total Knee Arthroplasty (TKA)

• Quad Strength = Primary impairment both Pre- and post-TKA
• 1st month post-op quad strength measure is affected more severely than other clinical measures such as ROM and Pain - 62% decline
  from pre-op strength
• High correlation between quad strength and improved functional performance

Mizner et al. JOSPT 2005;35:424-436.

Strength decreases associated with Immobilization
Muscle can lose 6 - 40% of its ability to generate force over a 4-6 wk period of immobilization

1. Mueller, Maluf, et al. Phys Ther. April 2003

• 110 subject randomized multicenter study of patients S/P ACL reconstruction
• Volitional EX only group –4 wk intervention attained 57% quad strength of uninvolved.
• NMES/vol EX group – 4 wk interv attained 70% or greater quad strength of uninvolved

Snyder-Mackler et al. J bone Joint Surg. 1995;77:1166-1173)

Small electrode

• Increases current density
• Recruits fewer motor units
• More uncomfortable

Large electrode (2.75" x 5")

• Recommended for this procedure

• Carrier frequency: 2500 Hz
• Frequency: 75 Bursts/sec
• On time: 10-15 sec
• Off time: 50-120 sec
• Amplitude: max tolerable, ↑ 50% MVC
• # of contractions: 10-15
• Sessions/wk: 3

Select “VMS™” or Symmetrical Biphasic

• Pulse duration: 400 µsec (note: phase duration= 200µsec)
• Frequency: 75 pulses/sec
• On time: 10-15 second contraction
• Off time: 50-120 second rest
• Amplitude: max tolerable, ↑ 50% MVC
• # of contractions: 10-15
• # of sessions/wk: 3

• Reversal of MM fiber type recruitment order. IIb-IIa-I (Trimble, Enoka Phys Ther. 1991;71:273-280).
• Over-riding of reflex inhibition
• SAID principle (overload)
  

• *Cardiac pacemaker
• Cardioverter defibrillator
• Over the carotid sinus/anterior transcervical area
• Over heart transthoracic area
• Over the abdominal, lowback and pelvic area during pregnancy
• Areas of venous or arterial thrombosis
• Thrombophlebitis
  

* See Belanger Evidence Based Guide to Ther Phys Agents. Lippincott Williams & Wilkins, 2003.

• Phrenic nerve or urinary bladder stimulator
• Neoplasm
• Superficial metal (e.g. staples, pins, external fixators)
• Patients prone to seizures
• Transcerebral stimulation
• Stimulation over the eyes
• Pain of unknown etiology
  

Contraindications Specific to NMES

• Musculotendinous lesion, in which tension on the tissue would create further damage.
• Absence of a secure bony attachment of the muscle e.g. avulsion fx