Web Posted on: December 18, 1998

Enhancing Physical Fitness in Spinal Cord Injured Individuals through New Technology

Pouran D.Faghri, MD
University of Connecticut

Introduction:

Chronic conditions and limitations of daily activities affect approximately 8.2 million American adults. Studies have shown that Fourteen percent of the United State population is affected by long term disabilities. The disability and limitations of function unable these individuals to carry out their normal life activities (1). Over the past 25 years the population of disabled have increased by 121% while the overall population grew only 43%. .

The estimated population of Spinal Cord Injured (SCI) in the United States is 200,000, with the projected increases of 6,000 each year (1-4). In addition, due to improvements in the medical technology and care, there will be more people approaching older age, therefore, chronic problems resulting in physical disabilities will become even more prevalent in the coming decades. Despite the mandates of American with Disability Act (ADA), access to the workplace and public facilities is still one of the major issues for the disabled population. This inaccessibility will eventually cause social isolation and related psychological and health problems in these people. The current fitness and recreational centers are not addressing the special needs of disabled population. While some of these centers assume that modifying their facilities to accommodate disabled population may not be economically sound, others found technical difficulties and feasibility of the required modifications as a barrier. To encourage investors to invest in designing new equipment and modifying their existing one, more critical research is required.

Producing enough scientific data on the effectiveness of new technology in improving physical fitness and overall quality of life for disabled population will eventually encourage the fitness and recreational facilities to accommodate the disabled population and make these facilities more desirable for these individuals.

The purpose of this paper is to give an overview of the current research in the area of exercise and physical fitness for SCI population. The use of Functional Electrical Stimulation (FES) to augment exercise capabilities of SCI individuals will be discussed.

Benefits of exercise programs for SCI: To meet the physical demands of every day life regular physical exercise has been recommended for able-bodied individuals. Regular physical exercise and improving physical work capacity is even more important for disabled population who already has limited physical and functional capabilities. Physical and psychological gains following exercise could improve overall health and quality of life for disable individuals. These improvements will eventually encourage the disabled person to actively participate in social life, make new friendships, face the stigmatization, reduce their risk of many chronic disease, and increased their potential of employment and productivity (6, 7).

Levels of exercise in SCI: Due to the paralysis of the lower leg musculature, SCI are usually depending on upper body exercises such as arm cranking and wheelchair propulsion for fitness training and locomotion. Therefore, for the assessment of the work capacity and maximum aerobic power upper - body exercise have been mostly recommended and used for these individuals. However, upper body exercise even for healthy able-bodied subjects is very stressful and may create major cardiovascular adjustments, which in the long term may not be to the person advantage. Cardiovascular adjustments following upper-body exercise are reduction in stroke volume (SV) and ventricular filling, and increases in total peripheral resistance (TPR), heart rate (HR), and blood pressure (BP). (9). The VO2 max during upper body exercise is also 30% less than VO2 max attained during leg exercises due to smaller muscle involve during arm exercise. These cardiorespiratory adjustments during arm ergometry will put a heavier demand on the heart (8-9) and may cause a life-threatening situation. An additional circulatory problem in the SCI is circulatory hypokinesis (i.e., a lower than expected cardiac output (CO) for a given oxygen uptake). This is basically due to blood pooling in the lower limbs secondary to paralysis of the leg muscles and inactivity of the venous "muscle pump". Studies have shown that SV and CO are 10-30% lower in SCI who perform upper-body exercise when compared with their non-disabled counterparts (6, 10-12). Circulatory hypokinesis may severely limit the upper-body exercise capacity of SCI due to compromises in venous return and cardiac output. This will further result in insufficient blood flow to the active muscles and reduce their exercise capabilities. Voluntary muscle contractions in the lower extremities of the SCI individuals are not possible, bringing their functional capacity even lower. Other measures of activating the larger lower extremity muscles are required to improve the fitness level of SCI population and to avoid unhealthy cardiovascular adjustments.

Functional Electrical Stimulation (FES) as a means of exercise:

What is electrical stimulation? The basic fundamental behind the electrical stimulation is the use of electricity to produce purposeful movement in the body. In person with SCI the communication system between the brain and skeletal muscle is interrupted. Most of the time, the motor nerve to the muscle is healthy and muscle is fully functional, but due to interruption at the spinal level, the information from the brain is never transmitted to muscle; and the muscle remains paralyzed for patient's entire life. Eventually, the dysfunctional muscle will became smaller and smaller as a result of disuse atrophy (6,10).

Electrical stimulation of the paralyzed muscles can be perform by simply putting appropriate electrodes over the muscle point and produce the required movements. Computerized functional electrical stimulation is now available to induce isokinetic and aerobic exercise for people with spinal cord injuries. Two systems have been primarily used for this purpose. One is the Cycle ergometer and the other is knee extension exercise. These devices can permit the large lower - limb muscles to be used and they may evoke high metabolic and cardiorespiratory responses, while activating the skeletal muscle pump. Below is a discussion of the some of the research on these two systems.

Training protocol:

FES-Knee extension (FES-KE): This device is a resistance knee extension exercise chair. A potentiometer is used for limb-position feedback to a microprocessor. This will cause a precise control of stimulator output during weight training. The stimulator voltage normally ranges between 0-150 V DC, with maximum current ouput of 150 mA. Two active and one passive electrodes are used for each quadriceps muscles. Most of the research followed the same protocol. Exercise normally was consisted of approximately five-knee extension - flexion cycles per minute. Each cycle was comprised of three seconds concentric quadriceps contraction followed by three seconds eccentric contraction followed by six seconds of rest. Knee joint range of motion was at 60 degrees. Weight training usually consisted of three exercise sessions per week with 30 minutes of exercise (15 minutes for each leg). Starting load was 1.5 Kg, with an increase of 0.5 Kg as performance improved to a maximum of 7 Kg. Training usually took 7 -12 weeks.

Cycle ergometer: The FES-induced cycle ergometer (FES-LCE), is a computer-controlled machine, which uses FES of quadriceps, hamstring, and gluteal muscles. FES is delivered via skin surface electrodes over muscle motor points to pedal at a target cadence of 50 rpm. The system uses a rectangular wave monophonic pulse 30 Hz, 0.375 msec duration up to 130-mA current to contract muscles. FES-LCE activates a larger muscle mass at substantially higher contraction frequency compare to the knee extension exercise. The contraction force however, is significantly lower than knee extension chair. Therefore cycle ergometry has been used mostly for endurance training. Exercise training usually has been three times per week, for 30 minutes. The starting power output has been 0 Kp (6.12 W) unloaded flying wheel for the first three sessions increasing by 1/8 KP Kp after completion of three times for each load up to 7/8 of kp.

Variables measured during knee extension exercise: 1) Muscle performance: was calculated as the mean product of resistive load (Kg) times the repetition performed during an exercise session. (Kg.rep), 2) muscle size: was measured at 10cm below the knee, 10 cm above the knee and 20 cm above the knee.

Variables measured during cycle ergometry: 1) power output: was calculated as the product of pedaling cadence (rpm), load (kp) and .98; 2) central hemodynamic measures including, cardiac output, stroke volume, heart rate, and arterial blood pressure were measured using impedance cardiography; 3) respiratory measurements including VO2 was measured using open circuit spirometry.

Results and discussion:

The results of most of the studies reviewed clearly indicated that several weeks of progressive FES-KE resistance training exercise of the quadriceps muscle not only induced hypertrophy, but also improve their strength and endurance. Our studies have shown significant improvements in muscle performance as well as increases in the leg girth at 10cm and 20 cm above the knee.

Exercise endurance level and power out put increased significantly following FES-LCE exercise training. After 12 weeks of training FES-LCE, power out put increased from 6 to 30 W, and exercise time increased from a few minuets to the 30 minutes target time. In a study by Pacy et al using computer tomography, an increase of 27% in the mid-thigh after 10 weeks of FES-KE exercise was reported. This increase corresponded with a significantly higher protein synthesis rate in the quadriceps muscle. In another study by Wilmot et.al, the rate of muscle loss has reduced by 20% following FES-induced isometric contractions of leg muscles. High levels of aerobic metabolic and cardiopulmonary responses was indicated by higher VO2 max following 12 weeks of training with FES-LCE. This data were supported by favorable central and peripheral hemodynamic responses (higher stroke volume, cardiac output, lower blood pressure and heart rate) following the training (10,11, 21). FES-LCE may cause contraction of the leg muscles during cycling and activates the skeletal muscle pump. Activation of the skeletal muscle pump will increase the venous return followed by increases in the pre-load of the heart and SV. Most SCI individuals will not be able to exercise with their arms at this high level of intensity for a sufficient duration (30 minutes) to stimulate marked cardiopulmonary adoptions. Therefore FES-LCE exercise provides individuals with SCI a means to potentially train at a similar aerobic metabolic rate as their able-bodied counterparts.

Peripheral circulation: As indicated before, deficit skeletal muscle pump activity and hypokinetic circulation in SCI can lead to several cardiovascular problem as well as reduced capacity for cardiopulmonary fitness training. Our studies have indicated that FES-induced rhythmic contractions of the calf and thigh muscles could improve the peripheral and central circulation. Our recent study shows significant increases in venous blood flow as indicated by higher ejection fraction following FES (15-20). These results confirmed that rhythmic FES technique could enhance peripheral and central circulatory responses. This may also alleviate venous pooling and excessive edema in the legs as well as orthostatic hypotension.

Conclusion

In conclusion, lower limb-FES- induced exercises can offer multiple therapeutic benefits for SCI individuals. These benefits are improved mental, physical and social health, as well as reduced secondary medical complications. It is important to note that participation in such exercises must be part of person's life style if optimal benefits are to be maintained. Unlike able-bodied individuals, who have the freedom to exercise at will, individual with SCI cannot perform any of these exercises without the specialized FES instrumentation, exercise facilities modifications, and a third person's help.

Some of the issues that need to be consider when exercising the individual with SCI: 1) make exercise and fitness centers more accessible to disabled individuals; 2) provide appropriate FES-exercise equipment; and 3) increase the research in this area specially longitudinal, well- controlled studies with large subjects to provide more evidence on its clinical efficacy.

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