Functional Electrical Stimulation Cycling for Spinal Cord Injury

Original Editor - Jessica Baglole, Janelle Girard, Alejandra Gomez, Miranda Umeri and Josh Nickel as part of the Queen's University Neuromotor Function Project

Top Contributors - Janelle Girard, Alejandra Gomez, Naomi O'Reilly, Kim Jackson, Jessica Baglole, Josh Nickel, Miranda Umeri, Aya Alhindi and Pacifique Dusabeyezu  

Overview

Functional Electrical Stimulation (FES) uses electrical pulses to stimulate motor neurons or denervated muscle fibers directly to elicit a contraction during a functional activity. FES has an extensive history for its treatment of orthopedic and neurological conditions. For example, FES can be used to activate tibialis anterior to help dorsiflex the foot throughout the gait cycle in patients with foot drop or to strengthen the quadriceps following a total knee arthroplasty.

FES Cycling applies the electrical stimulation to the muscles and/or nerves to contract the muscles associated with cycling. After a full rotation, each of the muscles will have been stimulated once with the appropriate timing and magnitude appropriate for cycling.  For example, Lower Extremity FES Cycling would activate the hamstrings, quadriceps, glutes and calf muscles. The muscles that are activated with Upper Extremity FES Cycling include the biceps, and triceps to name a few. The FES bicycle will detect changes in the muscle’s power output and will activate a motor when the muscles begin to fatigue to assist in the cycling. Over time, progress can be tracked by monitoring the amount of motor contribution.

FES Cycling may maximize the amount of function that is recovered through activity-dependent neuroplasticity as a result of the repeated exposure and stimulation of the nerves and muscles during the activity. FES Cycling 2-3 times per week for 10 weeks in individuals with a spinal cord injury showed increased total cycling power, endurance, lean muscle, and improvements in lower extremity ASIA Impairment Scales Scores for both Motor and Sensory, which is particularly important in individuals who experience the effects of chronic paralysis.

Individuals with a spinal cord injury face many barriers to participating in physical activity, which increases their risk for chronic conditions associated with a sedentary lifestyle. FES Cycling provides an accessible form of exercise for individuals limited in the ability to participate in other forms of exercise to evoke both the physical and psychological benefits that exercise can have.

Cost and Accessibility

There are at least three companies currently producing FES Bicycles in the United States.

1. Therapeutic Alliances, Inc., one of the oldest manufacturers, produce the ERGYS 3 Rehabilitation system for lower extremity cycling (therapeutic alliances).
2. Restorative Therapies, Inc. offers the RT300-S which can be operated directly from the individual’s wheelchair, eliminating the need for a transfer. Restorative Therapies supplies to USA, Canada, Australia and to other countries internationally .
3. Myolin produce the MyoCycle Home and MyoCycle Pro both designed for at home use. Given that it is the most affordable and simple to operate FES bike, it empowers people to use the bike and exercise without having to face barriers related to accessibility . The fee of the MyoCycle Home is $9,000 USD; includes everything you need to get started at home, including shipping, a 3 month supply of electrodes, and weekly progress reports via email. MyoCycle Pro is currently $13, 500 USD, and rental is available as well .

FES Bicycles, however, are not inexpensive and range from $9,000 USD to $30,000 USD  and are not covered by all private insurance companies. The general range for new bicycles is $16,000 to $30, 000 USD. Given the high cost of the device, many people access FES Bicycles through community settings. Physiotherapists and other qualified exercise professionals at specialized gyms or rehabilitation centres can help to apply the electrodes and calibrate the machine. Currently, there are few facilities with FES bicycles.

Benefits

Physical

• Increased cardiovascular fitness
• Metabolic influences by means of increases in capillary number, and increase in glucose metabolism
• Muscles increase in size, strength, and overall fiber area
• Increases in bone density and the ability to recover bone mass
• Improves and maintains active range of movement
• Increased power output
• Recover sensation
• Reduce spasm
• Improved glycemic control

Psychological

• Improvement in health from participating in regular exercise
• Individuals feel content seeing their leg muscles contract and being able to cycle
• Individuals can participate socially by cycling with others with similar conditions
• Improvements in overall quality of life

Risks

• Some individuals have an increased risk of autonomic dysreflexia when utilizing the bike
• Some individuals can experience increased spasm after use of the bike
• Injuries to the skin or joints (blisters, pressure sores, muscle tears, etc)
• Cycling provides a safer alternative than FES Walking as it reduces the risk of falling

Indications, Precautions and Contraindications

Indications

• Muscle Atrophy
• Cardiovascular Deconditioning
• Lower Limb Sensory and/or Motor Loss
• Bone Degeneration
• Spasticity

Contraindications

• Active deep vein thrombosis or thrombophlebitis
• Hemorrhagic Conditions
• Pregnancy
• Damaged or at-risk skin
• Cardiac Failure (Local)
• Infection (Local)
• Malignancy (Local)
• Recently Radiated Tissue (Local)
• Tuberculosis (Local)
• Electronic Device (Local)
• Impaired Circulation (Local)

Precautions

• Active Epiphysis
• Impaired Sensation
• Impaired Cognition
• Impaired Communication
• Skin Disease
• Regenerating Nerves
• Fatigue

Protocols

Frequency

FES Cycling typically requires frequencies of around 30Hz for effective stimulation. However, in order to optimize treatment, higher power output generated by the individual is ideal. For higher desired outputs, frequencies should be targeted at 50Hz - 60Hz for a 30 minutes exercise session. Fatigue, should not be an issue if the cadence is taken into consideration.

Cadence

Training plateaus may be common among individuals with a spinal cord injury using this type of treatment, which is usually due to a lack of progression of the exercise intensity. This is because FES causes rapid muscle fatigue compared to voluntary muscle stimulation. With faster-pedalling cadences (50 RPM), the maximum torque produced by the individual decreases quickly, compared to a slower pedalling cadence which produces higher power outputs. On the contrary, when cadence is slower (20 RPM), higher force is generated by the working muscles but the power production is decreased. Therefore, choosing the right cadence (20 RPM - 50 RPM) for training should depend on the individual’s goals to either increase power or increase strength.

Pulse Duration

Higher pulse durations, for example 350 and 500 microseconds, result in larger differences in energy expenditure (rest energy expenditure - exercise energy expenditure) compared to lower pulse duration of 200 microseconds. Small bursts of higher pulse durations did not have any meaningful differences compared to those mentioned above and seemed to trigger more symptoms of Delayed Onset Muscle Soreness (DOMS). It is important to be cautious when prescribing high pulse durations because these may trigger autonomic dysreflexia in an individual with a spinal cord injury above T6.

Treatment Intensity

The intensity may vary depending on whether the motor neuron is intact or whether the muscle needs direct stimulation to elicit a contraction. Denervated muscles require up to 100x more electrical energy to elicit a contraction of the muscle fibers. Currents used for functional electrical stimulation typically range from 120 MA to 300 MA, with the most commonly used parameter being 150 MA.

Electrodes and their Activation

There are different types of electrodes that can be used for FES Cycling. Electrical stimulation can occur through either implanted or surface electrodes. There are surface carbon electrodes, which are adhered to bicycle shorts and other electrodes that can be implanted in the body. While implanted micro-stimulators require surgery and are very costly, they can stimulate nerves of deeper muscles, such as iliopsoas. Using a larger sized electrode can be more comfortable for individuals, especially when more current is required for stimulation of denervated muscles. This is due to the fact that the current density is less when the surface of the application is larger. The main muscles that are stimulated include during FES Cycling: Quadriceps, Hamstrings, Gluteals, and the Calf Muscles. A  minimum of 6 electrodes are used to stimulate the muscles, which occur at different times depending on the angle of the leg throughout the cycle. An angle detector on the bike or the pedal will send information to the stimulation device in order to time the sequence of the leg contractions.