Functional electrical stimulation, or FES, is a therapeutic technique that applies low-level electrical currents to muscles and nerves. The purpose of this approach is to generate muscle contractions artificially. This process can help restore or improve bodily functions that have been compromised due to injury or illness. When the body’s natural communication pathway between the brain and a muscle is interrupted, FES provides an alternate route for the instruction to move, enabling a controlled, functional contraction.
How FES Activates Muscles
The body’s central nervous system naturally uses electrical impulses to command muscles to contract. These signals travel from the brain, down the spinal cord, and through peripheral nerves to reach their target muscle fibers. Neurological conditions or injuries can damage this pathway, preventing these signals from reaching their destination and leading to muscle weakness or paralysis.
Functional electrical stimulation works by bypassing this interruption. Small, adhesive pads called electrodes are placed on the skin directly over the specific muscle or the nerve that controls it. These electrodes are connected by wires to a stimulator device, which generates a controlled electrical charge.
This external current mimics the body’s own bioelectrical signals, prompting the nerve to fire an action potential. The signal travels along the nerve to the neuromuscular junction, where the nerve and muscle communicate. This triggers the release of neurotransmitters, causing the muscle fibers to contract. The intensity and timing of these contractions can be calibrated to produce useful movements.
Therapeutic Uses for FES
The applications for FES are centered on neurological rehabilitation, addressing conditions where the connection between the nervous system and muscles is impaired. It is frequently used for individuals recovering from a stroke, where it can help retrain motor pathways and improve limb function. Patients with spinal cord injuries may use FES to restore movement in paralyzed limbs, assist with standing, or power exercise machines. Other conditions where FES is applied include traumatic brain injury, multiple sclerosis, and cerebral palsy.
FES is also targeted toward specific functional goals. One of its most common uses is to treat “foot drop,” a condition where a person cannot lift the front part of their foot, which can lead to falls. By stimulating the nerve that controls the muscle at the front of the shin, FES lifts the foot at the appropriate moment during walking, creating a more natural and safer gait.
The technology also facilitates hand and arm movement, allowing individuals to practice grasping and releasing objects. In more advanced applications, FES can assist with bladder and bowel control by stimulating the pelvic floor muscles. It has also been adapted to aid respiratory function by stimulating the diaphragm, potentially reducing reliance on mechanical ventilators.
The FES Evaluation and Training Process
A patient’s journey with FES begins with an assessment by a physical or occupational therapist. The clinician evaluates the patient’s medical condition, muscle strength, range of motion, and skin integrity. This evaluation determines if FES is a suitable intervention and helps establish functional goals. For FES to be effective, the peripheral nerves connecting the spinal cord to the muscle must be intact.
Following the assessment, the therapist proceeds with device setup and calibration. This involves placing the electrodes on the skin over the targeted muscles and programming the stimulation parameters on the FES unit. The therapist adjusts settings like intensity, duration, and frequency to achieve a strong, comfortable muscle contraction. The timing of the stimulation is synchronized with a specific functional task.
Once the device is calibrated, the patient undergoes therapist-guided training sessions to learn to use the device while performing functional activities. For someone with foot drop, this might involve walking on a treadmill. For an individual with arm weakness, training could focus on practicing picking up objects. Many FES systems are designed for continued use at home, allowing patients to practice regularly and assist with daily routines.
Types of FES Systems
FES technology is delivered through two primary types of systems: surface and implanted. Surface FES systems are the most common and are non-invasive. These devices utilize electrodes that adhere to the surface of the skin over the target muscle group. The electrodes are connected to an external stimulator unit, which is often a small, portable device. This type of system is widely used for applications like treating foot drop or facilitating hand rehabilitation.
For more complex functional needs, implanted FES systems are an option. These systems involve a surgical procedure to place the electrodes directly on or near the nerves or muscles inside the body. The stimulator itself may also be implanted or remain external with signals transmitted wirelessly. Though more invasive, implanted systems can provide more precise stimulation for sophisticated applications like controlling bladder function or pacing the diaphragm to support breathing.