Functional Electrical Stimulation Cycling for Spinal Cord Injury

Introduction

Functional electrical stimulation (FES) uses electrical pulses to stimulate motor neurons or denervated muscle fibers directly to elicit a contraction (Berkelmans). FES cycling applies the electrical stimulation to the muscles and/or nerves to contract the muscles associated with cycling. For example lower extremity cycling would activate the hamstrings, quadriceps, gluteals and occasionally the calves (Berkelmans). The muscles that are activated with upper extremity FES cycling include the ____.

After a full rotation, each of the muscles will have been stimulated once with the appropriate timing and magnitude appropriate for cycling. Similarly, this can be done with an arm crank for upper limb training, it can also be done simultaneously with lower limb cycling as a hybrid exercise. (Berkelmans)

FES has an extensive history and evidence for its treatment of orthopedic and neurological conditions (Martin). For example, FES can be used to activate tibialis anterior to help dorsiflex the foot throughout the gait cycle in patients with foot drop. Electrical stimulation can occur through either implanted or surface electrodes (berkelmans). While implanted microstimulators require surgery and are very costly, they are able to stimulate nerves of deeper muscles, such as iliopsoas (Berkelmans). FES cycling may maximize the amount of function that is recovered through activity dependent neuroplasticity as a result of the repeated exposure and stimulation with activities that optimize neural activity and nerve regeneration (Martin). Griffin et al. (2009) observed 10 weeks of FES cycling 2-3 times per week with individuals with spinal cord injury (SCI). Results showed increased total cycling power, endurance, lean muscle, and improvements in lower extremity ASIA Impairment Scales scores for motor and sensory (Griffin), which is particularly important in individuals who experience the effects of chronic paralysis.

Individuals with a SCI face many barriers to participating in physical activity and are therefore at an increased risk for chronic conditions associated with a sedentary lifestyle (Ginis 2012). FES cycling provides an accessible form of exercise for individuals that are limited in their ability to participate in other forms of exercise to evoke both the physical and psychological benefits that exercise can have.

Indications

• Presence of Spasticity
• SCI with lower limb sensory and or motor loss

Protocols

Frequency: Functional electrical stimulation cycling typically requires frequencies of around 30Hz for effective stimulation. However, in order to optimize treatment, higher power output generated by the patient 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 cadence is taken into consideration .

Cadence: Training plateaus may be common among SCI patients using this type of treatment which is usually do to a lack of progression of the exercise intensity (Fornusek,2004). This is because FES causes rapid muscle fatigue compared to voluntary muscle stimulation. When pedalling faster (50 RPM), the max torque produced by the patient decreases quickly, compared to a slower pedaling cadence, however, higher power outputs are produced. (Fornusek, 2004). On the contrary, when cadence is slower (20 RPM), higher force is generated by the working muscles but the power production is decreased (Fornusek, 2004) Therefore, choosing the right cadence (20 RPM to 50 RPM) for training should be focussed on the individual’s goals either producing more power or increasing strength.

Pulse Duration: Higher pulse duration for example 350 and 500 microseconds results in larger difference in energy expenditure (rest energy expenditure-exercise energy expenditure) compared to lower pulse frequency of 200 microseconds (Gorgey & al. 2014). Small bursts of higher pulse duration did not have any meaningful differences compared to the mentioned above and seemed to trigger more symptoms of DOMS (delayed onset muscle soreness) (Gorgey & al. 2014). It is important to be cautious when prescribing high pulse durations because these tend to trigger, autonomic dysreflexia reactions in patients with SCI.

Treatment Intensity:The intensity may vary depending on if the motor nerve is still intact or whether the muscle needs direct stimulation to elicit a contraction.  Denervated muscles require up to 100x more electrical energy for contraction. (Berkelmans, 2008) Currents used for functional electrical stimulation typically range from 120 MA to 300 MA, the most commonly used parameter is 150 MA (Berkelmans, 2008).