Cardiorespiratory responses of patients with rheumatoid arthritis during bicycle riding and running in water.

Aerobic exercise has been shown to decrease the risk of heart disease, hypertension, and strokes and to be beneficial in the rehabilitation of patients with spinal cord injuries, heart disease, obesity, and diabetes.[1] More research, however, is needed to show the effects of exercise on individuals with arthritis.

Rheumatoid arthritis is a chronic inflammatory disorder of joints, resulting in joint pain, swelling and possible deformity, fatigue, and low physical working capacity.[2] People with rheumatoid arthritis are known to be deconditioned.[3] This deconditioning is thought to be caused by the primary effect of the disease on joints, the inactivity caused by muscle and joint pain, an overall cautiousness toward physical activity, or a combination of all these factors.[3]

In patients with arthritis, rest has often been the treatment of choice.[4] Rest is thought to reduce pain and inflammation and to preserve joint function.[4] As Smith and Polley stated, "We have been unable to find any evidence that active exercise beneficially affects the inflammatory processes of rheumatoid arthritis."[4](p143) Prolonged rest, however, is known to have detrimental effects on the cardiovascular/cardiomuscular system by decreasing stroke volume, muscle strength, blood volume, and muscle mass.[5] Investigators[6-11] have reported increases in cardiorespiratory fitness and muscle strength among people with arthritis after exercise training. There were no flare-ups of the arthritis during the training, and the active group of patients showed a better disease outcome.[10,11]

Because of joint pain, people with arthritis have often been limited in their ability to exercise. A mode of exercise that will produce a sufficient cardiovascular response to training, without muscle or joint pain limiting the intensity or duration of the exercise, would seem to be necessary for these patients. Water has been shown to be an excellent medium for reaching maximal exercise levels for people without impairments or disabilities,[12] as well as a means of exercise for pain reduction and range-of-motion exercises for people with arthritis.[13]

One purpose of our study was to compare the peak ventilatory and cardiovascular responses during dry-land bicycle ergometry and running in water while wearing a Wet Vest(*) in individuals with rheumatoid arthritis. (The Wet Vest, as shown in Figure 1, is a foam flotation device that is worn on the upper torso and secured with Velcro[R] straps.[dagger]) A second purpose was to determine whether the level of pain and perceived exertion during exercise are different at 60% of peak oxygen uptake ([Vo.sub.2]) and at peak [Vo.sub.2] in the water versus on the bicycle. We hypothesized that a higher peak [Vo.sub.2] and lower pain perception would be found in water exercise than in bicycle exercise. We also hypothesized that water exercise may elicit less pain and thus a higher peak [Vo.sub.2].

Method

Subjects

Eight women diagnosed with class II and III adult-onset rheumatoid arthritis[14] volunteered to participate in this study. The American Rheumatism Association class definitions are given in Table 1.[15] All subjects met the following criteria: were 30 to 40 years of age, were ambulatory without assistive devices, had no history of of cardiovascular dysfunction, had no acute tendinitis or bursitis, had knee range of motion of 5 to 110 degrees available, had no hip or knee surgery within the past 2 months, and had only minimal ankle limitations (ie, ankle range of motion of at least 10[degrees] of dorsiflexion to 30 [degrees], of plantar flexion). The subjects had a mean age of 35.88 years (SD = 2.85, range = 31-38), a mean weight of 66.75 kg (SD = 14.59, range = 41-84), and a mean height of 163.75 cm (SD = 8.9, range = 149-174). Medical consent was obtained for all participants.

Table 1.

Functional Classification of Individuals. With Rheumatoid Arthritis(a)

Class Definition

I    Complete functional ability, with ability to carry on all
     usual duties without handicaps

II   Functional capacity adequate to conduct normal activities
     despite handicap of discomfort or limited mobility of
     one or more joints

III  Functional capacity adequate to perform only a few or
     none of the duties of occupation or of self-care

IV   Largely or wholly incapacitated, with patient bedridden
     or using a wheelchair, permitting little or no self-care

(a) Established by the American Rheumatism Association.[15]

Data Collection

After reporting to the testing area, each subject gave informed consent. Descriptive data (ie, age, gender, height, weight, physical activity level, and health history) were collected on each subject. The testing procedure was then explained to each subject. The bicycle test was done first to ensure a safe environment for a maximal exercise test because electrocardiographic activity and blood pressure could be monitored. The bicycle test was also done first because of practicality, such as the location of the pool and the need to become familiar with the equipment.

Bicycle data. During the bicycle test, the following data were collected continuously. Heart rate (HR) was monitored using a Burdick EKG[double dagger] with a bipolar [V.sub.5] electrode configuration. Heart rate was recorded during the last 10 seconds of each 2-minute stage. Oxygen uptake was measured using a Vista CX desktop metabolic system.[8] The carbon dioxide and oxygen analyzer were calibrated prior to each experiment with micro Schollander analyzed gases according to the manufacturer's recommendations. Gas analysis was conducted in 30-second intervals. Validity of measurements obtained with indirect calorimetry, such as the measurements we obtained with the Vista metabolic system, has been demonstrated by correlating those measurements with those obtained with direct calorimetry.[16] Measurements obtained with the Burdick EKG from 10 subjects showed a Pearson product-moment correlation (r) of .99 when they were correlated with those obtained with the Sports Tester PE [3,000.sup.[parallel]].

During the last 10 seconds of each stage, pain was measured using a visual analogue scale (2.54-25.4 cm [1-10 in] long), with 1 equivalent to no pain and 10 equivalent to severe pain (Pearson r = .83).[17] Thirteen subjects completed the visual analogue scale to rate their pain. During the last 10 seconds of each stage, perceived exertion was measured using the Borg Rate of Perceived Exertion visual analogue scale (Fig. 2), ranging from 6 to 20 (Pearson r = .80).[18] Ratings of perceived exertion (RPE) for 16 subjects were correlated with two maximum fitness tests with different protocols of work intensities.

Water running data. The data collection for the water running test was similar to that for the bicycle test, except that HR was monitored from the carotid pulse. Measurements of the carotid pulse in a sample of subjects (N=15) were shown to be reliable and valid with the Burdick EKG (r=.99, P>.001).

Testing Procedure

Bicycle method. The procedures used in this study were similar to those used by Karper and Evans.[8] A maximal graded exercise test was done on a calibrated Monarch stationary bicycle.(#) Subjects had a 2-minute warm-up on the bicycle to promote familiarity with the procedure with 0 work load. Testing began at 150 kg.m/min, or W, at 50 rpm. The pedaling rate remained constant throughout the test. The work load was increased 150 kg.m/min by increasing tension on the flywheel at 2-minute intervals until the subject could no longer maintain the pedal rate due to fatigue or pain. Water running method. The procedures used in this study were similar to those used by Navia in an unpublished study.[19] After 48 hours but no more than 96 hours, each subject was tested in 1.5 m (5 ft) of water while wearing a Wet Vest (Fig. 1). The subject was tethered to the edge of the pool to ensure a stationary position that would facilitate collection of data (Fig. 3). The water level was at the subject's neck for all testing, with the subject suspended approximately 0.6 m (2 ft) off the bottom of the pool. The subject was encouraged to keep consistent lower-extremity length (ie, control of the amount of knee flexion during running) while running throughout the test. The subject then began simulated running while floating in a vertical position in 33[degrees] C water. The initial running cadence was set by a metronome at 92 beats per minute, shown in Navia's[19] study as being a comfortable beginning with low physiological impact (ie, a subject-reported Borg Scale rating greater than 10 and an HR less than 20 beats above the initial testing level), with each forward saving of the subject's leg corresponding to a metronome beat. The cadence was increased six steps per minute every minutes. The subject continued until the metronome cadence could no longer be maintained.

Data Analysis

Variables between bicycle riding and water running were tested using a paired t test. Significance was set at the 0.5 level.

Results

The characteristics for the eight subjects who participated in this study are presented in Table 2. The mean values and statistical probability values or level of significance for [Vo.sub.2], HR, pain, RPE, minute ventilation (Ve), respiration rate (RR), tidal volume (Vt), and respiratory exchange ratio (R) are presented in Tables 3 and 4. No differences were seen between the bicycle and water exercise for peak [Vo.sub.2], maximum HR, RPE at 60% of peak [Vo.sub.2], or pain. The peak RPE, however, was 22% higher in the water than on the bicycle. The peak R was 24% greater in the water than on the bicycle. The peak Ve on the bicycle was 26% larger than the maximal value obtained in the water, the peak RR in the water was 22% greater than that on the bicycle, and the peak Vt on the bicycle was 48% greater than that in the water. The Ve, Vt, and R were all different, but the RR was not different.

Table 2.
Characteristics of Subjects

Subject No.  Age(y)   Height(cm)   Weight(kg)   Gender
1             32        172        80           F
2             36        149        41           F
3             38        157        79           F
4             38        174        84           F
5             38        157        55           F
6             38        168        70           F
7             36        162        60           F
8             31        171        65           F

Table 3.
Mean Physiological Bicycle and Water Running Values(a)

                              Bicycle          Water
                              Ergometry        Running

Variable(a)                    X       SD      X        SD    P

[Vo.sub.2](mL/kg/min)        23.35    9.17    20.32    7.33  .11
HR (bpm)                    171.63   21.25   178.75   30.10  .38
Ve (L/min)                   63.09   13.88    50.06    8.87  .01
RR (breaths/min)             35.65    5.10    43.58   11.04  .06
Vt (L)                        1.76    0.29     1.19    0.27  .00
R ([Vco.sub.2]/[Vo.sub.2]     1.03    0.16     1.28    0.27  .02

(a) All values peak unless otherwise stated.
(b) [Vo.sub.2] = oxygen uptake, HR = heart rate, Ve = minute
ventilation, RR = respiration
rate, Vt = tidal volume, R = respiratory exchange ratio,
[Vco.sub.2] = volume
of carbon dioxide expired.

Table 4.
Bicycle Ergometry and Water Running Values for Mean Subjective
Responses

                      Bicycle          Water
                      Ergometry        Running

Variable             X        SD       X       SD      P

RPE(a) (peak)        17       2.45     18.13   1.73    .05
RPE (60%)            12.61    1.06     12.63   2.39    .99
Pain (peak)           5.25    3.45      4.38   4.17    .46
Pain (60%)            0.86    1.81      1.50   1.69    .64

(a) RPE = rating of perceived exertion.

The criteria for determining peak [Vo.sub.2] were reached in most tests.[20,21] These criteria are (1) maximum HRs must be at least 90% of the age-predicted maximum HR, (2) there must be a plateauing of [Vo.sub.2], and (3) R must be greater than 1.00.

In 75% of the tests, on the bicycle or in the water, two of the three criteria were met, indicating that a true peak [Vo.sub.2] was reached and that test order did not bias the results. Due to orthopedic limitations that could affect treadmill results, the subjects, peak [Vo.sub.2] during bicycle exercise may well be as high or higher than their treadmill results.

Discussion

Our study was undertaken to compare the [Vo.sub.2], HR, and other metabolic responses during dry-land bicycle ergometry and water running in individuals with rheumatoid arthritis. The mean peak [Vo.sub.2] on the bicycle of 23.35 mL/kg/min compares poorly with normative data of 30.1 mL/kg/min for a 70-kg person of this age group.[1] Our study is in agreement with earlier work by Ekblom et al[3] and Beals and colleagues,[22,23] who reported that people with rheumatoid arthritis are deconditioned. The mean value for [Vo.sub.2] during water exercise in our study was also relatively low (20.3 mL/kg/min) compared with the finding of m mL/kg/min in Navia's Wet Vest study[19] of fit individuals and the peak [Vo.sub.2] of 31.1 mL/kg/min for 48-year-old symptomatic individuals in Sheldahl's water cycling study.[24] The peak [Vo.sub.2] on the bicycle and in the water was higher than previously published values for people with arthritis[5,24]; however, those subjects were older than our subjects. Miller and associates[5] reported a 0.5-mL/kg/min decrease in peak [Vo.sub.2] per year after age 30 years. Making the appropriate adjustments in peak [Vo.sub.2] for age, the values in our study are very similar to findings of 15.9 mL/kg/min for 50-year-olds[24] and 18.8 mL/kg/min for 52-year-olds.[7] Several investigators[3,6,10] found peak HRs lower than those found in our study. Again, their subjects were older than our subjects. Heart rate response to exercise has been shown to decline 0.75% to 1% per year after peak physiological function is reached at about 30 years of age.[5]

The peak [Vo.sub.2] obtained on the bicycle (23.35 mL/kg/min) was higher, although not significantly higher, than the value obtained in the water (20.35 mL/kg/min). This finding agrees with the findings of previous studies comparing bicycle exercise with water exercise. Holmer and associates[25] found a 10% lower maximal [Vo.sub.2] during water exercise compared with during bicycle exercise, whereas McArdle and co-workers[26] found an 11% decrease in [Vo.sub.2] during water exercise. We hypothesized prior to our study, however, that water exercise may elicit less pain and thus higher peak [Vo.sub.2] values than bicycle exercise ill individuals with arthritis. Our subjects not only had lower peak [Vo.sub.2] values in the water but failed to experience less pain in the water at 60% of peak [Vo.sub.2] and at peak [Vo.sub.2]. Because our subjects were relatively young and had only recently been diagnosed with rheumatoid arthritis, joint pain may have failed to limit their performance on the bicycle. Thus, our initial hypothesis was not supported because joint pain was not a limiting factor. Older subjects with more advanced disease may have elicited different results, but data to support the hypothesis are lacking. Kline Mangione et al[27] investigated knee pain and exercise response to the effects of mechanical unweighting during treadmill exercise in 50-year-old individuals diagnosed with osteoarthritis. The subjects reported no difference in knee pain under any of the conditions. Thus, pain did not appear to be a limiting factor to exercise in these individuals.

Our subjects demonstrated a slightly higher HR in the water (4%) than on the bicycle, whereas Holmer et al[25] and McArdle et al[26] found lower HRs during water exercise than during treadmill running. Bicycle exercise has been shown to produce lower HRs than those produced during water running when the water temperature is relatively cool (27[degrees] - 29[degrees]C). Our study was done in water with a temperature of 33 [degrees] C. Studies by Holmer et al[25] and McArdle et al[28,29] have shown higher HRs during exercise in water with a temperature of 33 [degrees] C versus 27 [degrees] C or lower. These findings were believed to be due to the increase in peripheral circulation in the heated water.

Subjects had greater perceived exertion in the water than on the bicycle at peak [Vo.sub.2]. Svedenhag and Seger[30] found a higher RPE during running in 25 [degrees] C water than during treadmill running at a [Vo.sub.2] of 3.5 L/min and at an HR of 150 bpm. Although other factors such as ventilation and blood lactate probably affect RPE, HR may have had some influence on RPE in our study, which agrees with the correlation between Borg's RPE scale and HR.[31] Subjects had a slightly higher HR in the water. Even though this increase was not significant, it may have influenced the increase in RPE during water exercise. The RR was slightly higher during water exercise, which also may have influenced the increase in RPE in the water. In our study, the relationship between ventilation and RPE was unclear. The ventilation was higher during bicycle exercise, whereas RPE was higher during water exercise. One factor alone, apparently, does not affect RPE.

Ventilation was higher during bicycle exercise than during water exercise. This difference was due to reduced VT during water exercise. Sheldahl[24] reported similar results when comparing cycling on land and in 31[degrees]C water. Although he saw no difference in ventilation, he did see an increase in breathing frequency and a decrease in VT in the water. He believed that these findings were due to the engorgement of the lungs with blood during water exercise, causing a decrease in pulmonary compliance and a greater increase in breathing frequency than in VT. The increased blood flow to the lungs, he believed, was due to the hydrostatic pressure gradient in the water, causing a central shift in blood volume by a translocation of blood from the lower limbs and abdomen into the thoracic region.

An increase in R was seen in the water exercise compared with the bicycle exercise. Svedenhag and Seger[30] found R to be lower during maximal water exercise (1.10 [+ or -] 0.04) than during maximal treadmill running (1.20 [+ or -] 0.03). During submaximal exercise ([Vo.sub.2] of 3.0 L/min), R was higher in the water (0.982 [+ or -] 0.015) than on the treadmill (0.946 [+ or -] 0.010). Svedenhag and Seger also found higher blood lactate concentrations during water exercise at all levels of exercise. They believed that this higher anaerobic metabolism during immersion during submaximal exercise was partly due to a lowered perfusion pressure in the legs during running in water, with a resultant decrease in total muscle blood flow. Svedenhag and Seger gave no explanation for the difference shown during maximal exercise. This difference could be explained by the higher anaerobic metabolism reached on the treadmill, shown by the increase in the volume of carbon dioxide expired, resulting in a higher R on the treadmill. Without data on lactate levels, it is difficult to make any such conclusions in this study, but the hydrostatic pressure in the water could affect R at submaximal work loads. Heat-related stress caused by the temperature of the water in this study (33 [degrees] C versus 25 [degrees] C in the study by Svedenhag and Seger[30]) could cause a subject to hyperventilate; thus, more carbon dioxide would be blown off and R would than be greater at maximal work loads in the water.

The mean percentage of the peak [Vo.sub.2] obtained during bicycle exercise that was reached during water exercise ([peak [Vo.sub.2] during water exercise/peak [Vo.sub.2] during bicycle exercise] X 100) was 85%. The lowest percentage of the peak [Vo.sub.2] obtained during bicycle exercise that was reached by any subject during water exercise was 68%. Both of these values are well above the minimum of 40% set b, the American College of Sports Medicine (ACSM).[32] The ACSM's established guidelines for improving cardiorespiratory fitness are 40% to 85% of maximal [Vo.sub.2]. Because subjects were able to reach exercise levels well above the ACSM guidelines (45% above) in the water, they should be able to sustain the needed 40% for 30 minutes. This hypothesis was supported by an unpublished study involving the same subjects. In that study, McLauchlin and associates[33] showed that this population had a good adherence rate and a 100% compliance rate in a 6-week water training study. These data, however, have not been published in a peer-reviewed format.

Our results indicate that both methods of exercise obtained training levels, as stated by the ACSM,[32] that would affect the cardiovascular system. Neither mode of exercise caused an exacerbation of the subjects, pain. In circumstances in which physiological testing values cannot be measured, RPE has been shown to be a reliable and valid measurement method for obtaining information about training intensity.[18,34] The ACSM recommends exercising at an RPE of between 13 and 17 on the Borg Scale, for appropriate training levels.[32] We believe that it is important to instruct these types of patients to monitor their pain to ensure that there are no adverse effects from exercise, although research has shown that there should not be any adverse effects. These forms of exercise, ill theory, could be used with older individuals with rheumatoid arthritis, although their lower-extremity range of motion may affect their ability to ride stationary bicycles. Both methods of exercise appear to be capable of achieving the necessary training levels for older individuals, while providing a comfortable, less painful environment in which to exercise.

Conclusion

We believe that water exercise can be a useful mode of exercise for individuals with rheumatoid arthritis because it allows them to reach the needed training levels, as established by the ACSM,[32] within a comfortable environment. In our study, however, there was no difference in pain level and perceived exertion was greater during water exercise than during bicycle exercise. Pools are considered to be a valuable tool in the treatment of individuals with rheumatoid arthritis. They also may prove to be an alternative to the stationary bicycling for aerobic exercise. Aerobic exercise is necessary for this population to help reduce their weight and improve their cardiovascular fitness, while not increasing their pain. Further research is needed to evaluate the benefits of water exercise for individuals with severe rheumatoid arthritis.

References

[1] Lamb DR. Physiology of Exercise Responses and Adaptations. New York, NY: Macmillan; 1984.

[2] Berkow R. Talbott JH, eds. The Merck Manual 13th ed. Rahway, NJ: Merck Sharp and Dohme Research Laboratories; 1977.

[3] Ekblom B, Lovgren O, Alderin M, et al. Physical performance in patients with rheumatoid arthritis. Scand J Rheumatol. 1974;3:121-125.

[4] Smith RD, Polley HF. Rest therapy for rheumatoid arthritis. Mayo Clinic Proc. 1978;53:141-145.

[5] Miller PB, Johnson RL, Lamb LE. Effects Of four weeks of absolute bed rest on circulatory function in man. Aerospace Med. 1964;35:1194-1200.

[6] Ekblom B, Lovgren O, Alderin M, et al. Effect of short-term physical training on patients with rheumatoid arthritis, I. Scand, J Rheumatol. 1975;4:80-86.

[7] Harkcom TM, Lampman R, Banwell BF, Castor CW. Therapeutic value of graded aerobic exercise training in rheumatoid arthritis. Arthritis Rheum. 1985;28:32-39.

[8] Karper WB, Evans BW. Cycling program effects on one rheumatoid arthritic. Am J Phys Med. 1986;65:167-172.

[9] Nordemar R, Berg U, Ekblom B, Edstrom L. Changes in muscle fibre size and physical performance in patients with rheumatoid arthritis after seven months, physical training. Scand J Rheumatol. 1976;5:233-238.

[10] Nordemar R. Physical training in rheumatoid arthritis: a controlled long-term study, II: functional capacity and general attitudes. Scand J Rheumatol. 1981;10:25-30.

[11] Nordemar R, Ekblom B, Zachrisson L, Lundqvis K Physical training in rheumatoid arthritis: a controlled long-term study, I. Scand J Rheumatol. 1981;10:17-23.

[12] Whitley JD, Schorne LL. Comparison of heart rate responses: water walking versus treadmill walking. Phys Ther. 1987;67:1501-1504.

[13] Steigelman G, ed. Arthritis Foundation YMCA Aquatic Program. Champaign, Ill: Human Kinetics Inc; 1985.

[14] Steinbrocker O, Traeger CH, Batterman RC. Therapeutic criteria in rheumatoid arthritis. JAMA. 1949;140:659-662.

[15] Arnett FC, Edworthy SM, Bloch DA, et al. The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis. Arthritis Rheum. 1988;31:315-324.

[16] Montoye HG, Kemper HCG, Saris WHM, Washburn RA. Measuring Physical Activity and Energy Expenditure. Champagne, Ill: Human Kinetics Inc; 1996.

[17] Woodforde JM. Merskey H. Some relationships between subjective measures of pain. J Psychosom Res. 1972;16:173-178.

[18] Skinner JS, Hutsler R, Bergsteinova V, Buskirk R. The validity and reliability of a rating scale of perceived exertion. Med Sci Sports. 1973;5:94-96.

[19] Navia AM. Comparison of Energy Expenditure Between Treadmill Running and Water Running. Birmingham, Ala: The University of Alabama at Birmingham; 1986. Thesis.

[20] Adams GM. Exercise Physiology Lab Manual. Dubuque, Iowa: Wm C Brown Communications Inc; 1990:67

[21] Taylor HL, Buskirk E, Henschel A. Maximal oxygen uptake as an objective measure of cardiorespiratory performance. J Appl Physiol. 1955;8:73.

[22] Beals CA, Lampman RM, Figley BA, et al. The oxygen cost of work in rheumatoid arthritis patients. Clin Res. 1980;28:752A. Abstract.

[23] Beals CA, Lampman RM, Banwell F, et al. Measurement of exercise tolerance in patients with rheumatoid arthritis and osteoarthritis. J Rheumatol. 1985;12:458-461.

[24] Sheldahl LM. Effect of head-out water immersion on cardiorespiratory response to dynamic exercise. J Am Coll Cardiol 1987;19:1254-1258.

[25] Holmer I, Stein EM, Saltin B, et al. Hemodynamic and respiratory responses compared in swimming and running. J Appl Physiol. 1974;37: 49-54.

[26] McArdle WD, Glaser RM, Magel JR. Metabolic and cardiorespiratory response during free swimming and treadmill walking. J Appl Physiol. 1971;30:733-738.

[27] Kline Mangione K, Axen K, Haas F. Mechanical unweighting effects on treadmill exercise and pain in elderly people with osteoarthritis of the knee. Phys Ther. 1996;76:387-394.

[28] McArdle WD, Magel JR, Lesmes GR, Pechar GS. Metabolic and cardiovascular adjustment to work in air and water at 18 [degrees], 25 [degrees], and 33 [degrees]C. J Appl Physiol. 1976;40:85-90.

[29] Craig AB, Dvorak M. Comparison of exercise in air and in water of different temperatures. Med Sci Sports. 1969;1:124-130.

[30] Svedenhag J, Seger J. Running on land and in water: comparative exercise physiology. Med Sci Sports. 1992;24:1133-1160.

[31] Borg GAV, Noble BJ. Perceived exertion. Exerc Sports Sci Rev. 1974;2:131-153.

[32] Pate RR, Blair SN, Burstine JL, et al, eds. ACSM Guidelines for Exercise Testing and Prescription. 4th ed. Philadelphia, Pa: Lea & Febiger; 1991:96.

[33] McLauchlin L, Werk DR, Walter J, et al. Effects of Suspended Water Jogging on Individuals With Class II and III Rheumatoid Arthritis. A Pilot Study. Birmingham, Ala: The University of Alabama at Birmingham; 1989. Thesis.

[34] Borg G. Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med. 1970;2:92-98.

(*) Bioenergetics Inc, 2790 Montgomery Hwy, Pelham, AL 35124-9977. ([dagger]) Velcro USA Inc, M Brown Ave, PO Box 5218, Manchester, NH 03108. ([double dagger]) Burdick EKG, 15 Plum St, Milton, WI 53563. ([section]) Vacumetrics Inc, Vacumed Division, 5770 Nicolle St, Ventura, CA 93003. ([parallel]) Polar Electro OY, Hukamaantie 18, SF-90440, Kempel, Finland. (#) Monark-Crescent AB, Box 503, 432 01 Varberg, Sweden.