Exercise is linked with numerous health benefits; however people with spinal cord injury (SCI) are limited in their ability to perform adequate exercise due to loss of function below the injury level. One method to improve exercise intensity after SCI is through functional electrical stimulation (FES) exercise. FES exercise, combined with voluntary upper extremity movements, provides whole-body exercise in this population which would otherwise be impossible. . Rowing is an ideal activity for people with SCI because it requires activation of the posterior shoulder muscles, which are typically weak in people with SCI. Adaptation of an existing rowing machine for FES requires integration of electrical stimulators, a switch and bracket system to control the stimulators, and other seating and stability options. The final design was well received by people with SCI and shows promise for increasing exercise intensity and improving shoulder muscle balance.
Exercise and physical activity are associated with many health benefits including reduced cardiovascular disease, reduced risk of cancer, improved mental health, and increased life expectancy(1). Adults with spinal cord injury (SCI) have lower rates of aerobic fitness than the general population and are at increased risk of disease, diabetes, and obesity and have high rates of shoulder pain which may be due to lack of strength in the posterior shoulder (2), (3). Therefore, it is necessary to improve aerobic fitness after SCI without causing an increase in shoulder pain. Functional electrical stimulation (FES) exercise is a promising mode of training for adults with SCI because it provides the ability for leg exercise in a population with loss of function below the level of injury. In FES exercise, surface electrodes are applied to specific muscle groups in order to induce involuntary contractions, allowing individuals with SCI to perform coordinated leg motions. FES has been commercially adapted for exercise bikes and two companies in the United States produce FES bikes (4), (5). However, FES biking is performed either only with the legs, or in conjunction with a voluntary upper body arm crank ergometer (ACE). Full body exercise provides an increased cardiorespiratory demand compared to arms-only exercise, however FES rowing has been shown to be better tolerated and produce a greater cardiovascular demand than combined cycling. Additionally, the rowing motion of the upper body may be beneficial for improving muscle imbalance and shoulder pain in this population. Existing FES rowing machines present three design issues: 1. The rowing stroke is uncoordinated and does not allow for a long smooth stroke, 2. Participants often require remedial FES strength training for up to 12 weeks prior to initiating FES-row training, and 3. Seating systems lack stability for people with higher-level injuries.
The primary objective of this project was to adapt a commercial indoor rower into an FES rower, by incorporating two electrical stimulators which activate the leg muscles with proper rowing form. Stimulation of only one muscle group should occur at any time. At maximum leg extension, the electrodes on the quadriceps should turn off and the electrodes for the hamstrings should turn on; at maximum knee flexion, the opposite should occur. FES rowing should not require remedial training to strengthen leg muscles and the seating system should provide adequate support for people without voluntary trunk control.
The Concept 2 Dynamic Indoor Rower was chosen for this project. Unlike most commercial rowers which have a static footplate and a dynamic seat which moves in accordance with the rowing motion, the Concept 2 Dynamic model rower has a static seat and a dynamic footplate. This difference removes the requirement that the person rowing must have enough leg strength to push against the footplate and propel their body backwards along the seat track. This, in turn, removes the need for remedial strength training before individuals with SCI can use the FES rower.
Functional Electrical Stimulation
In order to adapt the Concept 2 Dynamic rower into an FES rower, electrical stimulation must be delivered to the leg muscles. Electrical stimulation is delivered by two Medtronic Respond II Dual-Channel electrical stimulators through eight surface electrodes, two to each muscle group (quadriceps and hamstrings) and can be adjusted between 0 and 100 mA until muscle contraction occurs. For proper form, electrical stimulation must alternate between application to the hamstrings and the quadriceps. To achieve this, a make/break circuit was created between two single-pole double-throw (SPDT) pushbutton switches and two 2.5 mm mono audio connectors for electrical stimulator control. When the circuit between the switches and electrical stimulators is made, electrical stimulation is delivered to one of the muscle groups, and when the circuit is broken, electrical stimulation is delivered to the other. To control the circuit, two SPDT switches were placed along the footplate track of the Concept 2 rower. When the legs and the footplate are at maximum flexion or extension, the footplate contacts a switch and the current alternates from one muscle group to the other, reversing the direction of leg movement. Lastly, a double-pole, double-throw (DPDT) toggle switch is located between the pushbutton switches and allows for easier setup of the FES rower by the administrator (Figure 1).
Two brackets were also manufactured to position the pushbutton switches onto the Concept 2 Dynamic rower. These brackets were required to remain adjustable in order to accommodate individuals of different heights. An upper steel L-bracket mounts the switches and a lower aluminum bar, in combination with two eye bolts for each bracket, locks the switches in place along the footplate track. Non-identical brackets were created due to different sizing constraints on the front and rear of the rower. Initially aluminum was considered for the upper L-bracket but testing showed it deformed under rowing conditions so the thicker steel was necessary to resist rowing forces (Figure 2).
Seating and Support Solutions
Additional items implemented for seated stability on the Concept 2 Dynamic rower include addition of leg supports from NuStep, an improved seat from Creating Abilities, and an assortment of Therabands and springs to the rower. The leg supports and seat act to improve the posture of the seated user and keep the user’s legs positioned in proper rowing form. The springs and Therabands help reverse the leg motion when the direction of stimulation is alternated; these are especially useful if the user experiences spasticity with knee extension.
Finally, the footplate and handle of the Concept 2 rower have been mechanically decoupled. In its original design, the footplate and handle provide opposing forces to allow both arm and leg contribution to drive the flywheel of the rower but for people with SCI, this coupling provides too much resistance for the leg extension movement and hinders FES rowing. In order to provide a decreased amount of resistance for leg extension, the springs and Therabands serve a dual purpose by providing a force for the legs to push against, while assisting in return of the footplate during the knee and hip flexion phase. Each spring and Theraband can be exchanged for a stronger or weaker version depending on the needs of the user (Figure 3).
The Concept 2 rower cost $1,400, the seating and stability components cost about $1,000, and the FES switch and bracket system cost about $60 (Table 1). This work aims to purchase and adapt a rower into an FES rower so the total cost was $2,452.46. For individuals seeking to adapt currently owned rowing machines to FES rowers, such as rehabilitation facilities and gyms, the cost is greatly reduced to about $60 plus the cost of the electrical stimulators and any required seating and stability adaptations. As the price for the brackets is inflated by purchasing material in bulk, the cost to produce the brackets can be reduced through mass production.
Recruitment for a study investigating the benefits of FES rowing for people with SCI has begun at the University of Alabama at Birmingham. Using this design, the objectives for adapting a commercial rower into an FES rower have been achieved. First, the adapted rower electrically stimulates the hamstrings and quadriceps in proper rowing form. Second, the FES rower allows participants to row from day 1 because the legs are separate from the arms and the footplate moves instead of the seat. Finally, user feedback reports that the Creating Abilities adaptive canoe seat and the NuStep leg supports achieve their seating and stability needs.
Table 1. Itemized account of all costs to adapt a Concept 2 Dynamic rower into an FES rower.
This design achieves all specified objectives and allows people with SCI to achieve a full body exercise with an FES rower. Feedback from users with SCI also point to improvements on the current design. Users would prefer to have grab bars on either side of the seat to ease transfers to and from their wheelchair and for pressure relief maneuvers. Users would also prefer improvements to the electrode set-up so that they can independently set-up the electrical stimulators. Lastly, a motorized footplate would be preferred to support the motion of the legs when fatigue occurs. Overall, the current device is generally well tolerated and enjoyable.
Concept 2 has embraced adaptive rowing and has allowed their devices to be retrofitted for FES rowing in competition at the CRASH-B indoor rowing competition (6). Potential for the company to incorporate components of the FES rower into a commercial FES rower is high.
Special thanks to the client Susan Silverman for design help with this project and to Dr. Alan Eberhardt for his mentorship and support. This project was sponsored by the Department of Physical Therapy at the University of Alabama at Birmingham and the National Institute on Disability and Rehabilitation Research (NIDRR #H113E120005).
1. Center for Disease Control. Physical Activity and Health. Retrieved from http://www.cdc.gov/physicalactivity/everyone/health/
2. Fekete, C., and Rauch, A. (2012). Correlates and determinants of physical activity in persons with spinal cord injury: A review using the International Classification of Functioning, Disability, and Health as a reference framework. Disability and Health Journal, 5(3), 140-50.
3. Burnham, R., May, L., Nelson, E., Steadward, R., and Reid, D. (1993). Shoulder pain in wheelchair athletes: the role of muscle imbalance. The American Journal of Sports Medicine, 21, 238-242
4. Therapeutic Alliances Inc. Retrieved from www.musclepower.com
5. Restorative Therapies. Retrieved from www.restorative-therapies.com
6. C.R.A.S.H.-B. World Indoor Rowing Championship. Basic Information: Able-bodied and Adaptive Events. Retrieved from http://www.crash-b.org/web/2014-regatta/basic-information/