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Functional electrical stimulation, a two-year study.


Vrbova (1963); Brown, Cotter, Hudlicka & Vrbova (1976); Peckham, Mortimer & Marsolais (1976); Petrofsky & Phillips (1983); Petrofsky, Phillips & Hendershot (1985); Petrofsky & Smith (1988, 1991); and Van der Meulen (1974) all examined the use of electrical stimulation as a means of reversing the atrophy of skeletal muscle associated with paralysis. The ultimate goal of this research, including later work on computer-aided movement (Marsolais & Kobetic, 1982; Petrofsky, Glaser, Phillips & Gruner, 1982; Petrofsky, Phillips & Hendershot, 1985; Petrofsky & Smith, 1992) was to restore lost motor function (Guttman, 1976) and reverse some of the secondary medical problems associated with spinal cord injury such as pressure sores, kidney and bladder infections, and bone fractures (Young, 1982; Foege, 1985). In fact, these secondary medical problems are the most significant problems associated with spinal cord injury in terms of both cost and medical complications. It is not uncommon for a paralyzed individual to expend between thousands and tens of thousands of dollars in medical costs each year (Guttman, 1976; Burke, 1975; Young, Burns, Bowen & McClutcheon, 1982).

Pressure sores, for example, have a yearly rate of incidence of over 30% (Young, Burns, Bowen & McClutcheon, 1982). Freehafer and Mast (1965) have shown that bone fractures have an incidence of 9.3%. It is hoped that functional electrical stimulation (FES) may offer a means of reversing some of these secondary medical problems through exercising paralyzed muscle and increasing the blood delivery to the legs.

However, questions arise as to the safety of the technology. In weak, osteoporotic bone, can powered muscle stimulation cause bone fractures in itself? What is the incidence of electrode burns with continuous FES use? Further, the compliance of a patient population for this technology must be examined. This was the purpose of the present investigation.


The subjects in these studies were 109 volunteers. Eighty-three of the subjects in these studies volunteered to participate in research. These individuals were asked to participate for a minimum of a two-year period. Twenty-six subjects were involved in a broad-based clinical program involving FES and conventional therapy. The average age of the research group was 26 +/- 3 years, whereas the average age of the clinical group was 29 +/- 9 years. Of the research group, 40 were persons with quadriplegia and 43 were persons with paraplegia. All were diagnosed as having complete injuries. All protocols were shown to each subject. All procedures were approved by the committee on human experimentation.


Four exercise modalities were used here as described below:


Upper body conditioning of non-paralyzed muscles (weightlifting) was accomplished on specially designed equipment. Special handles and arm grips were used so that persons with quadriplegia could accomplish upper body weightlifting.

FES Weightlifting

Functional Electrical Stimulation (FES) weightlifting involved electrical stimulation of the paralyzed muscles in the body. Electrodes were applied above the muscle, and transcutaneous electrical stimulation was used to excite the motor nerves to elicit a muscle contraction.

To exercise a given muscle, a weight was applied that would resist the movement of that muscle through loading of its joint. Electrical stimulation was then applied with biphasic, square-waves at a pulse width of 350 microseconds and a stimulation amplitude, which was variable, from 0 to 150 milliamps. The frequency of stimulation was 35 Hz. As current was increased through the stimulation electrodes, the muscle contracted. Current was adjusted so that the muscle lifted a weight over a period of three seconds, held the weight for one second, and then slowly reduced the amount of force in the muscle over another period of two seconds; six seconds were allowed between the contractions. The exercise was continued for 15-minute periods. If exercise could be maintained for 15 minutes, then the weight was increased by one pound the next day. In contrast, if the exercise fatigued the muscle in less than 10 minutes, one pound was removed prior to the next day's exercise.

Computer-controlled Bicycling

Bicycle ergometry was accomplished on a modified Monarch bicycle ergometer similar to one described by Petrofsky, Glaser Phillips and Gruner (1982) and Petrofsky and Phillips (1983). The bicycle, as shown in Figure 1, was modified with a highback seat and seat belts to allow paralyzed individuals, such as the girl shown in this Figure, to sit comfortably. A new bicycle seat was designed because a conventional bicycle seat has too small a seat base to allow posture to be stable in someone with lower body paralysis. Additionally, the size of a conventional seat base puts high pressure on the pelvic area, an area where over 50% of all pressure sores occur (Young et al., 1982). Knee stabilizer bars were added to the sides of the legs so that exercise could be accomplished without abduction or adduction of the hips. A digital computer controlled the timing of the onset of the electrical stimulation to the quadriceps, hamstring and gluteus maximus muscles. The stimulation pulse width was 350 microseconds, and biphasic square-wave stimulation was used. The current was adjusted to as high as 180 milliamps at a frequency of 35 Hz. to maintain a pedaling speed of 50 rpm. If the speed was below 50 rpm, then the stimulation current was increased. In contrast, if the speed was too high, the stimulation current was decreased by the computer program.

Computer-Controlled Walking

As shown in Figure 2, some individuals were involved in computer-controlled walking programs. Computer-controlled walking (Petrofsky, & Phillips, 1983; Petrofsky, Phillips and Hendershot, 1985; and Petrofsky & Smith, 1991) involved electrical stimulation of the hamstring, quadriceps and gluteus maximus muscles during walking in a modified Louisiana State University reciprocating gait orthosis. Electrical stimulation was applied at a frequency of 30 Hz and a pulse width of 350 microseconds to allow movement of the legs during walking. The current was varied to 100 milliamps, but typically averaged about 60 milliamps during ambulation.


Clearly, there were two separate groups of individuals in these studies. The research group participated in a laboratory-based series of experiments. Here only one type of exercise was done over the two-year period and all exercise was done in the author's laboratory. The clinical group was engaged in a clinical rehabilitation program which involved three and one half months of physical therapy followed by a home program involving exercise two days a week for approximately two hours each day. The clinical group did all exercise modes listed above but less intensively than the research group. A summary of the programs is given below.

Research Programs

Of the 83 individuals who participated in research, 40 were persons with quadriplegia and 43 were persons with paraplegia. All individuals were diagnosed as having a complete spinal cord lesion. Of this group, 22 participated in weightlifting studies, 28 in bicycling studies, and 33 in studies involving computer-controlled walking. For FES weightlifting studies, individuals exercised their quadriceps muscles with FES three times per week, with the weight slowly being progressed until a maximum of 50 pounds was reached. After that time, they reduced their participation to 2 times per week to maintain muscle mass. This was the only exercise this group accomplished during that year. For the individuals involved in FES bicycling, following a four-week training period of the quadriceps muscles with FES weightlifting as described above. FES bicycling was accomplished three times per week with each bicycle session lasting 30 minutes. Resistance was progressively increased so that individuals fatigued at the end of the 30-minute period. This exercise was continued for the remainder of the two years. Finally, the 33 individuals who were involved in FES walking participated for one year in FES weightlifting and bicycling prior to walking. This protocol involved one month of FES weight training of the quadriceps, gluteus maximus and hamstring muscles, as described above, so that the strength of the muscles would equal or exceed 10 pounds of force during weightlifting. This was followed by FES bicycle training until they could pedal the bicycle against a load of 3/8 KP for 30 minutes. They then entered a walking program after completing the weight training and bicycling programs and 3 months of standing in a standing frame one hour a day, three days a week. Walking involved two months of training on how to walk in the Louisiana State University reciprocating gait orthosis. Once brace training was complete, FES walking was begun. This involved using a combination of electrical stimulation and ambulation in the RGO. Walking involved ambulation in the braces while stimulation was applied to the quadriceps, hamstring and gluteus maximus muscles to provide movement of the legs. Individuals in this group walked for a minimum of 1 mile per week and also exercised twice a week on the FES bicycle ergometer.

Clinical Program

The clinical program was conducted at the Petrofsky Centers for Rehabilitation and Research in Irvine, California. The clinical program required a medical screening examination which was conducted prior to the admission of an individual into the program. Screening included a pulmonary function test, ECG and ECG stress tests, clinical chemistry profile, a complete physical examination, a neurological evaluation, MRI's and X-Rays. Individuals then began the program with two weeks of passive physical therapy (range of motion and stretching) and one hour a day standing in the standing frame. Range of motion and standing frame continued for the first two months of the program. However, after two weeks, electrical stimulation was started on the quadriceps, hamstring, gluteus maximus, gastrocnemius and tibialis anterior muscles in the paraplegic groups. Quadriplegic groups underwent the same program of electrical stimulation. In addition, they received stimulation of the deltoids, biceps, and triceps, finger flexors and finger extensors. FES weightlifting was continued for the first two months of the program. During the third month, FES bicycling was started. After 3-1/2 months in the program, individuals participated in gait training in the FES walking system (Petrofsky and Smith, 1991). After 4-1/2 months from the beginning of the program, individuals graduated from the full-time program and began a home program. The home program involved functional electrical stimulation with a home computer-controlled stimulator of the quadriceps, hamstring and gluteus maximus muscles, as well as computer-controlled walking. Weightlifting was accomplished against loads of 10 pounds on each of the muscle groups listed above two times per week. This home exercise regime required approximately 2 to 2-1/2 hours per day on each of the exercise days. Every six months individuals returned back to the main program for a physical evaluation to assure that the progress was satisfactory and to see how they were complying with the program.



The compliance of the subjects in the two programs is shown in Table 1. The number of people who started in each program is shown as well as the number of people remaining in the program at one month, three months, one year and two years later. For the clinical group, very few people left the program. After two years, approximately 90% of the people who started remained. In contrast, of the 83 people who started with the research group, only 42% of the people remained in the program.



START 83 26
1 MONTH 81 24
3 MONTHS 80 24
1 YEAR 71 24
2 YEARS 35 23

Interestingly enough, in this group, the majority of the people who dropped out were the persons with paraplegia and not the persons with quadriplegia. Most persons with quadriplegia in the research group (83%) remained throughout the entire length of the study.

Injuries Associated with

Functional Electrical Stimulation

Over the two-year period that functional electrical stimulation was used, injury records were kept of bone fractures and electrode burns. Table 2 shows the incidence of electrode burns. In the clinical group, only one electrode burn was found in the first month of the study. No electrode burns were seen after this time. In the research group, three burns were found in the first month, one burn in the second, and an additional burn in the third month of the study, and no burns thereafter.


START 83 26
1 MONTH 3 1
3 MONTHS 1 0
1 YEAR 0 0
2 YEARS 0 0

During the two-year period that these studies were being accomplished, there were three documented bone fractures in the research group. One was directly related to the actual FES research. The other two fractures were caused by accidents outside of the laboratory environment. In the clinical group, one documented fracture was found out of the 26 people who were examined in these studies. This fracture occurred during FES weightlifting.

Strength and Endurance

Individuals who participated in the research studies showed a dramatic increase in endurance and strength. In the research bicycle group, for example, individuals who could only pedal a bicycle ergometer at the onset of the studies for a period of a few seconds were able to pedal the bicycle ergometer for an hour at a load of up to 1 kp at the end of the two-year period. For the average quadriplegic and paraplegic, the endurance increased from 15 +/- 11 and 11 +/- 7 sec on the first day of bicycling against a load of zero kp to 27 +/- 4 min. and 29 +/- 3 min. at a load of 0.7 +/- 0.1 NS 0.8 +/- 0.2 kp for the two respective groups. With the clinical group, although training was only 3 months long, bicycling endurance increased from a few seconds to the ability to work against loads of 0.3 +/-.04 and 0.3 +/- 0.05 kp for 28 +/- 3 and 29 +/- 4 min. in the quadriplegic and paraplegic groups respectively.

In a similar manner, muscle strength increased in both research and clinical groups. At the end of the two-year period, the pooled data of the research group showed that the average subject in the research group was able to lift 35.6 +/- 11.1 lbs with the quadriceps muscles sustained for the 15-minute exercise regimes described above, whereas the average person in the clinical group could only lift 12.3 +/- 1.4 lbs. for a 15-minute exercise period. These differences were statistically significant (p) when comparing data on the paraplegic research group to that of the paraplegic clinical group or comparing the data on the clinical and research quadriplegic groups.

Health Care Benefits

In both the research group and clinical group, health care benefits were examined. During the year before individuals participated in these studies, the number of bone fractures, pressure sores, and kidney and bladder infections were recorded. The same parameters were measured during the two-year study period. Data on individuals who dropped out of the program were not used in this statistical data base. The results of these measurements are shown in Figures 3 and 4. Figure 3 compares the incidence of pressure sores for the entire group of subjects (clinical and research) for the year before (pre) and the two-year study period. Pressure sores were reduced by over 80% during the exercise program period in all groups comparing the data collected in the year prior to the two years of the study. Bone fractures were also dramatically reduced when people exercised in the FES exercise program (see Figure 4). Finally, bladder infections were reduced from an incidence of 62 +/- 11 % in the pre group to 34 +/- 6% in the trained groups (pooled data). All of these differences were statistically significant( P-0.01).


Individuals engaged in either research or clinical programs, showed high compliance in maintaining the program through a period of two years. The individuals who engaged in clinical programs had much higher compliance than those in the research programs. The reason this probably occurred is that the clinical program was only of 3-4 months duration, followed by a home program. In contrast, the research program required 24 months of laboratory participation, making it harder to be a subject in since it required individuals who participated to stay at the laboratory each week for a two-year period. Further, the clinical program had a better balance in terms of doing exercise on all the major muscle groups in the body than the research program where only one type of exercise was done for two years. This variability of allowing people to do different things each day made the program much more interesting, according to the participants.

FES exercise appeared to be fairly safe to accomplish. In both groups of research and clinical subjects, the incidence of bone fractures was lower than the national average of people not engaged in any type of rehabilitation. Further, the incidence of electrode burns was not only low, but after the first few months when people were better acquainted with the equipment and how to use electrodes and electrode paste, electrode burns were no longer a problem for this group of over 100 individuals.

Since pressure sores account for two-thirds of all medical costs associated with spinal cord injury in individuals who have been injured for two or more years, anything that will reduce the incidence of pressure sores is very important to accomplish (Young 1982). The National Transportation Safety Board commissioned the National Research Council to write a study, "Injury in America" in 1985. The National Research Council identified research on pressure sores to be of greatest importance in relation to victims of auto accidents because of their significant medical and financial implications with all aspects of paralysis. The dramatic reduction in pressure sores associated with the functional electrical stimulation training program may be caused by a number of different things. First of all, they may be caused by changes in lifestyle. Pressure sores are commonly caused by inactivity. Individuals engaged in these types of exercise programs begin to get out more in the community, take on a more active role in life, such as going back to their education, and jobs. Additionally, the increase in peripheral blood flow and the resultant delivery of oxygen to the limbs, must have a telling effect. Since 50% of all pressure sores occur in the pelvic area, the increase in muscle mass and muscle girth associated with functional electrical stimulation in itself would add padding to bony prominences. The combination of an increase in blood flow and increased muscle mass may be a significant factor in reducing the incidence of pressure sores.

The results of this study suggest that functional electrical stimulation can be well tolerated by paralyzed individuals. In clinical programs, the compliance is very high. Exercise can be done safely and results in positive health care benefits to the patient. However, it must be emphasized that these studies were only conducted on a limited number of individuals and over a period of two years. Further study is warranted.


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Title Annotation:Physical Function
Author:Petrofsky, Jerrold S.
Publication:The Journal of Rehabilitation
Date:Jul 1, 1992
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