Functional Electrical Stimulation (FES) is a device that applies synchronised electrical currents to neural tissue to restore a degree of control over abnormal function (Ragnarsson, 2008). It can be used in functional motor activities including walking, standing transfers and hand grasping. The use of FES for rehabilitation of Spinal cord injuries is effective in keeping preserved neurological function and reflexes to near normal physiological state (Ragnarsson, 2008). FES addresses 3 main tasks;
- Improves function of weakened muscles
- Correction of incorrectly performed movements
- Acquisition of a movement habit approximating the normal
(Vitenzon, Mironov, & Petrushanskaya, 2005)
Indications for FES in SCI patients
FES is the electrophysical agent of choice when presented with deficiencies in motor function which alters or prevents normal functional movement. Spinal cord injuries (SCI) are largely the cause of such functional deficit which is commonly seen in;
- Complete or partial loss of supraspinal control
- Leads to spasticity and paresis
- Lesions in the spinal motor neuron system, spinal roots and peripheral nerves
- Causes moderate flaccid paralyses of limbs
- Insufficiency of afferent control
- Diseases and lesions to the support/movement system
- Secondary muscle atrophy and weakness in muscles
(Vitenzon, Mironov, & Petrushanskaya, 2005)
Application of FES in SCI patients
In order for FES to be applied, patients with SCI must have;
- Relatively preserved nervous control of muscle activity (efferent and afferent)
- Incomplete loss of function of the excitation and contraction response to electrical stimulation
- Sufficient joint mobility for the movement concerned
- Potential for partial or complete recovery of movement
(Vitenzon, Mironov, & Petrushanskaya, 2005)
The application of FES has shown to be most beneficial in patients with incomplete spinal lesions however there is some evidence indicating small positive effects for patients with complete spinal lesions.
Figure1: FES used to help SCI patients hold, grip and pick up objects (http://www.sciencecodex.com/)
Figure 2: FES used to correct foot drop in gait training in SCI patients ( http://www.mstrust.org.uk/)
Parameters
NMES and FES are often used interchangeably in conversation and in fact both apply identical principles and operate on similar parameters. One can say that the FES is simply the use of NMES to electrically stimulate paralysed muscles in a sequence that correlates with a functional task. Although NMES may lead to enhanced function it does not necessarily provide function like FES (Sheffler & Chae, 2007).
Waveform: Balanced biphasic waveform is commonly used clinically to ensure control over force of muscle contraction and decreases the risk of tissue damage (Ragnarsson, 2008). This waveform was also used in gait rehabilitation in patients with lumbar sacral lesion of the spinal cord.
Amplitude: Amplitude and duration dictates the number of nerve fibres activated and force of the muscle contraction. This parameter is generally determined by the patient’s level of tolerance to the electrical stimulus. 60-70V amplitude or 250mA current depending on the setting (CV/CC) was the set intensity used in SCI gait rehabilitation (Vitenzon, et al., 2005).
Frequency: Must be high enough for a smooth muscle contraction. In order to stimulate a neuromotor response, a medium frequency of 35-70Hz is sufficient however this may vary with different functional task performed. 50-60Hz was effectively used in the gait rehabilitation in patients with SCI (Vitenzon, et al., 2005).
Pulse Duration: Short pulse duration of approximately 350 µsec has proven to be comfortable and enough to stimulate a motor response in sensate patients. 30-250 µsec was used in SCI patients during gait rehabilitation (Vitenzon, et al., 2005).
Ramp:
- Up - 1 second
- Hold contraction – depends on type of training (endurance requires a longer contraction >8 sec with less rest and 3 sets of 12-15 reps)
- Down – 1 second
- Rest between contractions – 1, 3, or 5 seconds
Now I hope you have a bit of an idea of what FES is all about, keep looking for our next blog when we will delve deeper into the use of FES for spinal cord injury rehabilitation.
REFERENCES
- Ragnarsson, K. T. (2008). Functional electrical stimulation after spinal cord injury: current use, therapeutic effects and future directions. Spinal Cord, 46(4), 255-274.
- Sheffler, L. R., & Chae, J. (2007). Neuromuscular electrical stimulation in neurorehabilitation. Muscle Nerve, 35(5), 562-590.
- Vitenzon, A. S., Mironov, E. M., & Petrushanskaya, K. A. (2005). Functional electrostimulation of muscles as a method for restoring motor functions. Neurosci Behav Physiol, 35(7), 709-714.
