Functional Electrical Stimulation (FES) is the electrical stimulation of nerve pathways to produce a controlled contraction of muscles. This controlled muscular contraction can improve the function and mobility of the limbs in many patients with damage to the upper Spinal Cord or nerves. These lesions are found in patients with Multiple Sclerosis, stroke, head and spinal trauma etc. The most suitable cases for application of FES are where the lesions are above the level of the lowest rib, generally lesions below this level tend to have damaged the nerves where they exit the spinal column, and as a result of this damage to the peripheral nerves the electrical impulses cannot travel to the muscles, and therefore FES is not effective. The electrical stimulation is generally applied through electrodes attached to the skin, positioned so as to stimulate the required nerves.

FES can also be used as an exercise system for paralysed muscles in order to increase muscle bulk, improve blood flow, and improve skin condition. In many cases patients have reported reductions in spasticity of opposing muscle groups, as a side benefit of using FES.
 
The most common application is for correcting "Dropped Foot Syndrome", where the patient is unable to lift the foot, using  a small portable electrical stimulator. This stimulator is about the same size as a mobile telephone, and is worn clipped to the belt of the patient.

By electronically stimulating the common Peroneal nerve at its most superficial point, where it passes over the head of the Fibula bone, it is possible to cause the required muscles of the lower leg to contract and thus the foot to lift.
This may also cause the excitation of the withdrawal reflex and then the knee and hip joints may flex to varying degrees. These two actions when carefully controlled will improve the walking action in many cases. Timing of the stimulation is achieved through the use of a pressure sensitive switch which is positioned beneath the heel of the affected limb.

The actual sensation experienced is similar to "pins and needles" which the user quickly becomes accustomed to. Wires to the electrodes are worn beneath the clothing, and the whole set-up is very unobtrusive. More complicated problems with the mobility when walking can be addressed using a multi channel stimulator to work on more than one group of muscles, or both limbs simultaneously.
 
It also possible to use functional electrical stimulation to stimulate the muscles of the upper limbs, particularly in the case of stroke patients. This can bring about improvements in the mobility and motility of the limbs, and can be particularly useful for correcting subluxation of the shoulder. Hand and arm function can be improved in many cases, enabling the carrying out of many day to day tasks.
 
There is also evidence of a "carry over effect" where patients who have used FES for a prolonged period, have reported an improvement in the muscle and limb function when unaided by FES. This has been more prominent in Stroke patients, but some Multiple Sclerosis patients have also reported similar improvements.
 
The use of FES requires the patient to fulfil certain criteria, in particular, there should be no significant medical complications such as Epilepsy, or poor skin condition, hypersensitivity to the electrical stimulation is also contra-indicated. Where using basic functional electrical stimulation to enable improvement in walking, the patient should be able to stand, and have a certain degree of mobility (either unaided or with the use of a balance aid). Patients need to be mentally unimpaired as they will need to be able to understand the methods of use of the devices, and generally the better the motivation of the patient the better the results. The use of FES does require some initial training of the patient but most are soon able to use the equipment effectively, and to very good effect.

After the initial fitting and customisation of the stimulator, the progress of the user needs to be monitored on a regular basis, in order to adjust the timing and level of stimulation required to maximise the benefits of the treatment.
 
Although at present most stimulation is carried to the nerve through surface applied electrodes, the use of electrodes implanted into the muscles is being developed. This however tends to be used upon the more seriously impaired patients. This and continued development in the FES field will mean great improvements for many people with neuorological damage within the coming years.