Effects of aerobic exercise on pain perception, affect, and level of disability in individuals with fibromyalgia.

Key Words: Aerobic exercise, Affect, Disability, Fibromyalgia, Pain perception.

Fibromyalgia is a nonarticular rheumatic disease of unknown origin diagnosed by the presence of widespread pain accompanied by tenderness at 11 or more of the 18 specific tender point sites.[1] These tender points are primarily localized to the musculotendinous junctions.[2] Symptoms include generalized fatigue; chronic headache; sleep disturbances; patient-reported joint swelling without objective findings of swelling; irritable bowel; neuropsychiatric symptoms; numbness; and modulation of symptoms by activity, weather, and stress.[1] This disorder is most common in women between 20 and 50 years of age, with an estimated incidence of 3 to 6 million.[3-5]

Standard medical and physical therapy interventions have been relatively ineffective in the treatment of this disorder.3 Some relief of symptoms has been noted from treatment with amitriptyline and cyclobenzaprine.[6,7] Two recent studies by McCain and colleagues[8,9] have suggested that cardiovascular training is beneficial in reducing the symptoms of fibromyalgia, including the reduction of pain ratings, improvement in the level of the disease activity, and improvement in the psychological profiles of the participants. Subjects in both of these studies participated in a 20-week exercise program, consisting of either cardiovascular training (using bicycle ergometers) or flexibility exercises. The findings of these two studies suggest that both types of exercise may reduce the symptoms of fibromyalgia (pain thresholds, pain ratings, patient reports of disease activity, and physician assessment of disease activity), but cardiovascular training produced slightly greater results.

The finding that cardiovascular fitness could reduce the symptoms of fibromyalgia is not surprising. Aerobic exercise has been reported to decrease pain perception and improve the affects of both patient and nonpatient populations.[8-12] Running has been found to result in diminished pain ratings during the run[10] and hypoalgesic responses to ischemic and thermal pain following the run in trained runners.[11] Additionally, post-run testing on the Mood Visual Analogue Scales has demonstrated affective changes, characterized by elevated scores for joy, euphoria, cooperation, and conscientiousness.[11] In a recent study of patients with rheumatoid arthritis, a 6-week aerobic program decreased morning stiffness and joint tenderness but did not change overall pain reports.[13] Gun,[12] in a case study, found that a 20-minute run relieved migraine headaches in a patient who found no pain relief with standard aspirin treatment. The initial study of patients with fibromyalgia conducted by McCain[8] revealed that psychological profile improvement was greater in the cardiovascular fitness group; however, the subsequent study by McCain et al[9] demonstrated no difference between the final psychological profiles of the cardiovascular fitness and flexibility training groups.

McCain[14] hypothesized that cardiovascular fitness might benefit the pain and affective symptoms of fibromyalgia via activation of central or peripheral beta-endorphin systems or release of adrenocorticotropic hormone (ACTH) or cortisol. Elevated serum beta-endorphin has been associated with bicycle ergometer training in patients with rheumatoid arthritis.[13] The patients, however, demonstrated no change in pain ratings. Nonetheless, elevated beta-endorphin levels have been associated with changes in pain and affective ratings in long-distance runners.[11] Release of ACTH and cortisol occurs in response to any stressor, of which exercise in excess of 60% of maximal oxygen consumption is one.[15] This release of beta-endorphin, cortisol, or ACTH, therefore, might be responsible for the changes in affect and pain ratings reported by McCain and colleagues.[8,9]

Bennett[16] has hypothesized that the chronic fatigue reported by individuals with fibromyalgia results in a relatively sedentary lifestyle and, thereby, a decrease in the fitness level of skeletal muscles. Consequently, the muscles may be more susceptible to microtrauma from any exercise activity, which then produces the pain associated with this syndrome.[16] Similarly, a disturbance of the microcirculation of the involved muscles in individuals with fibromyalgia has been identified.[17] Aerobic exercise may (1) increase the resistance of a trained muscle to microtrauma, (2) improve the individual's sense of being in control of his or her body, and (3) improve circulation within muscles.[16,17] These changes may be responsible for the improvements in pain ratings and psychological scores reported by McCain and colleagues.[8,9]

The studies by McCain and coauthors[8,9] demonstrated that bicycle ergometry for progressively longer bouts and at a level sufficient to raise each subject's heart rate to greater than 150 beats per minute reduced the symptoms of fibromyalgia. This is a relatively high level of aerobic activity and may not be appropriate for all individuals with fibromyalgia. Bicycle ergometry is also only one means of achieving cardiovascular fitness. As is suggested by Klug et al,[18] further research is needed to determine what other types of exercise, as well as the duration and intensity of that exercise, are necessary to produce similar results. The studies by McCain and colleaguess[8,9] both used a 20-week exercise protocol. This is a fairly long program, making recruitment and retainment of subjects difficult.

The purpose of our study was to evaluate the role of an 8-week aerobic walking program, as an alternative aerobic activity, on the pain ratings, affective components, and level of disability ratings of individuals with fibromyalgia. An increase in heart rate to 60% to 70% of the predicted maximum heart rate for age for a period of 20 minutes was used to define the activity as aerobic. The American College of Sports Medicine has identified this level of activity as sufficient for the development or maintenance of cardiorespiratory fitness in healthy adults.[19] Walking is an inexpensive and convenient form of exercise, easily performed without equipment in almost any setting. Furthermore, walking can be easily maintained at a constant intensity and demonstrates minimal interindividual variability in energy expenditure.[19] We hypothesized that subjects participating in the aerobic walking program would demonstrate a greater decrease in pain and disability ratings and a greater improvement in affective ratings than sedentary subjects.

Method

Subjects

Twenty-four subjects were recruited from the Central Ohio Fibromyalgia Association (Columbus, Ohio), a support group for patients with fibromyalgia. Diagnosis of primary fibromyalgia, according to the American College of Rheumatology criteria,[1] was confirmed by each subject's own rheumatologist or physiatrist. If this could not be done, the subject was reevaluated by a physiatrist as part of this study. Persons with a history of heart disease, lung disease, uncontrolled hypertension, or orthopedic disorders that would preclude aerobic activity were excluded from the study. Individuals who were participating in or had participated in any regular aerobic exercise program within the 6-month period preceding the selection of subjects were also excluded from the study. Additionally, all subjects were interviewed regarding activity level and reported a relatively sedentary lifestyle for at least 6 months prior to participation in the study.

Because only two men volunteered for the study and there was a large variability in the age of the volunteers, subjects were first matched for age and gender and then randomly assigned to either an experimental group or a control group to control both age and gender as a source of variance. Matching involved pairing those closest in age and then assigning one member of the pair to each group. The two men in the study were within 1 year of the same age and, therefore, were easily matched as a pair. The experimental group ranged in age from 31 to 64 years [bar] X=47.8, SD=11.08), and the control group ranged in age from 30 to 69 years ([bar] X=50.8, SD=11.83). All subjects except one reported experiencing pain and muscle symptoms for greater than 10 years. One subject in the control group reported experiencing symptoms for only 4 years. Patients were asked to refrain from taking nonsteroidal anti-inflammatory, pain, hypnotic, and antidepressant medications (including aspirin) during the course of the study. Compliance was confirmed by verbal report. After the procedures and risks were explained to the subjects, written informed consent was obtained.

Exercise Program

Subjects in the experimental group participated in an 8-week walking program, three times per week. Each session included a warm-up and cool-down regimen of stretching exercises, 1 warm-up and cool-down lap of slow-paced walking, and 20 minutes of fast-paced walking on an indoor track. During the fast-paced walking, subjects exercised at 60% to 70% of the predicted maximum heart rate for their age, as monitored by midsession recordings of heart rates obtained by palpation for 30 seconds. Pacing by the researchers and volunteers was used to ensure that subjects maintained the same pace, monitored by maintaining the same lap (once around the track):unit time (in seconds) ratio. The American College of Sports Medicine reports that heart rate will remain relatively constant during an activity that is maintained at a given level.[19] Walking at the same pace, therefore, should maintain the heart rate at the same elevated level. Heart rates and blood pressures were also taken prior to and following each exercise session to establish baseline levels and ensure appropriate return to baseline levels after exercise.

Subjects in the control group were sedentary, continuing with daily activities but not participating in any exercise program. These subjects met only to fill out questionnaires prior to and after the 8-week program. No other contact with other subjects was included. These subjects were not asked to keep an activity log, but verbal reports from these subjects were consistent with the description of this group as sedentary throughout the 8-week period. None of the control group subjects were participating in any formal or informal type of exercise, and none reported any change in activity level at work or home during this period.

Instrumentation

Prior to and after the 8-week program, subjects in each group completed the McGill Pain Questionnaire (MPQ), the Sickness impact Profile (SIP), and the Brief Symptom Inventory (BSI). All of these measures have been found to be valid and reliable instruments for their respective uses.[20-22] The MPQ provides two indexes of pain: (1) the total number of items chosen and (2) the pain rating index (PRI), which is an index of the severity of the items chosen. The SIP was used to evaluate the level of disability. It provides a Psychosocial Dimension scale score and a Physical Dimension scale score, indicative of the level to which the disorder is affecting the individual's lifestyle. The BSI is a psychological profile, consisting of 53 questions and providing nine subscales: somatization, obsessive-compulsive, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychoticism. It also provides three global indexes: the General Severity Index (GSI), the Positive Symptom Distress Index (PSDI), and the Positive Symptom Total (PST).

Data Analysis

Pretest and posttest scores on each of the three self-report measures were computed for each subject. These included two scores for the MPQ (total number of items chosen and the PRI), three global scores for the BSI (GSI, PSDI, and PST), and two global scores for the SIP (Physical Dimension scale score and Psychosocial Dimension scale score). Despite random assignment of subjects to the two groups, the subjects in the experimental group had higher initial scores on all of the measures except the PST of the BSI. Because initial scores were found to correlate highly with the final scores on each instrument, an analysis of covariance was used to analyze the posttest scores, adjusting for the initial difference in the pretest scores.

Results

General Findings

Nineteen subjects, 10 experimental group subjects (1 man, 9 women) and 9 control group subjects (1 man, 8 women), completed the 8-week study. Five subjects, 2 from the experimental group and 3 from the control group, did not complete the study. The 2 subjects in the experimental group dropped out due to changes in their schedules that prevented them from attending the exercise sessions. The 3 control subjects did not return for the final testing. The pretest data from these subjects, therefore, were excluded from the analyses. All subjects in the experimental group were able to achieve the designated 60% to 70% of the predicted maximum heart rate for their age by the end of the second week of the walking program.

Due to initial differences in the pretest scores on all measures between the two groups, posttest scores were adjusted, using analysis of covariance. Initial posttest means, standard deviations, and adjusted posttest means are depicted in the Table.

Pain Perception

The experimental group demonstrated lower, but not significantly lower, scores on both indexes of the MPQ, choosing fewer items and less severe items, as indicated by the PRI, than the control group.

Affect

The experimental group scored lower on both the GSI and the PST of the BSI than did the control group; the latter difference was significant (P<.05) (Fig. 1). Mean adjusted posttest scores on the PSDI were almost identical for the experimental and control groups (58.8 and 56.8, respectively).

Disability

The global measures computed for the SIP reflect the level that the subject's disability is influencing the physical and psychosocial aspects of his or her life. The experimental group demonstrated higher Physical Dimension scale scores on the posttest (P<.05) (Fig. 2) and lower, but not significantly lower, Psychosocial Dimension scale scores than the control group.

Discussion

This study was undertaken to evaluate the potential benefits of an aerobic walking program on the symptoms of fibromyalgia, including the pain perception, affective components, and level of perceived disability. The results, as reported, are inconclusive. Although subjects who participated in the aerobic walking program scored lower on five of the seven measures, only the score on the PST of the BSI was statistically significant. Furthermore, significantly higher physical disability scores were found on the SIP. Therefore, even though the trends suggest that this type of program may have some beneficial effects, the lack of significant findings makes any recommendation of exercise as a treatment modality difficult. The adjusted final means for the Physical Dimension scale of the SIP identified a significant difference between the exercise group and the sedentary group, reflecting higher scores for the exercise group. This finding suggests that exercising three times per week may increase the level of perceived physical disability. Items in this scale of the SIP address the impact of the disability on ambulation, body care, and mobility. It is possible that perceived increases in muscle stiffness or fatigue resulting from the exercise program affected the experimental group subjects' responses on this scale.

The Physical Dimension scale scores for both groups, however, were substantially lower than those reported for other chronic pain disorders. Follick et al[23] reported mean scores of 17.7 for patients with chronic low back pain and 14.0 for patients with rheumatoid arthritis. The adjusted final means for the subjects in our study were 9.21 and 5.67 for the experimental and control groups, respectively. This finding suggests that the fibromyalgia syndrome had not altered the physical lifestyles of these subjects to the same degree as other patients with chronic pain.

The Psychosocial Dimension scale scores on the SIP were similar to those of other patients with chronic pain,[23] Suggesting that fibromyalgia affects the social interactions of these patients more than their physical lifestyles. Furthermore, the experimental group demonstrated a trend toward better psychosocial function on the SIP after the 8-week program, compared with the control group. This finding was consistent with the lower levels of psychological distress reported on the GSI and PST of the BSI.

During the course of the 8-week exercise program, the experimental group subjects, who met three times per week, began to develop some social and emotional ties to control group subjects. Anecdotal reports by the subjects suggested that these changes may have contributed to the improved psychological profiles of the experimental group subjects. They reported that they enjoyed participating in the exercise sessions, as well as the group support that they received during these sessions. In addition, the exercise sessions provided an opportunity for them to talk to others about their condition. Although this could be an additional benefit for any group exercise program, it may have contributed to the improvements noted for the experimental group on the psychological dimensions. Because the control group did not meet regularly, the group differences noted may have been at least partially attributable to the social support of the group exercise sessions.

Factors that may have contributed to the limited significant findings in this study are the small sample size, variability in the activity of the control group subjects, and variability in the exercise performance of the experimental group subjects. Because our study involved a relatively small sample size, a large effect size was necessary to produce significant findings. The lower scores identified on the two indexes of the MPQ, the GSI and PST of the BSI, and the Psychosocial Dimension scale of the SIP for the experimental group might have reached significance with a larger number of subjects. Although verbal reports from the control group subjects did not indicate any changes in activity levels, it is possible that an increase or a decrease in physical activity did occur. A third issue is that although pacing and a midsession monitoring of heart rate were used to ensure the level of exercise was at 60% to 70% of the predicted maximal heart rate for each subject's age, intersession and intrasession variability may have existed. Finally, it is possible that the level of exercise chosen (60%-70% of the predicted maximal heart rate for each subject's age), the duration of the exercise (both for the individual sessions and the length of the study), and the frequency of the exercise were insufficient to produce significant changes in the measurements.

Summary

Our study lends some support to the initial findings of McCain and colleagues,[8,9] who reported that a cardiovascular fitness program improved pain ratings and psychological profiles of individuals with fibromyalgia. McCain and coauthors used a 20-week program of exercise at a higher level of aerobic capacity than we did. These differences in exercise protocol may have contributed to the findings of our study.

The exercise program in our study was designed to elevate the participants' heart rate to 60% to 70% of the predicted maximum heart rate for their age for 20 minutes, which has been found to produce cardiovascular fitness in nondisabled subjects.19 All subjects were able to achieve their designated level by the end of the second week of the program, and they were able to maintain a pace at which this rate was achieved for 20 minutes during each of the sessions in the remaining 6 weeks. Because no specific test of cardiovascular fitness was conducted, the reported changes cannot be attributed solely to changes in cardiovascular fitness levels. Furthermore, beta-endorphin, ACTH, and cortisol are reported to be released in response to exercise at aerobic levels (60% of maximal oxygen consumption). Exercising at a level sufficient to increase a subject's heart rates to 60% to 70% of the predicted maximum heart rate for his or her age, however, should yield an increase in oxygen consumption of only 42% to 56% of maximum capacity.24

No research is available to suggest that exercising at this lower level will activate the release of beta-endorphin, ACTH, or cortisol. Therefore, it is unlikely that the release of these substances can explain the pain and affective scores obtained in our study. This level of exercise may be sufficient to increase the individual's fitness level as well as to improve the microcirculation to the involved muscles, and thus decrease the occurrence of microtrauma and pain. Bennett also suggests that this effect of exercise is associated with a sense of "being in control of one's body,"[16] which could be associated with the improved psychological scores obtained for the experimental group subjects in our study.

The inconclusive findings of our study necessitate further evaluation of this type of program for use as a treatment for individuals with fibromyalgia. Future research should ensure (1) social interaction for sedentary subjects or isolation of exercising subjects; (2) a greater number of subjects to minimize the effects of initial group differences and maximize experimental variance; (3) evaluation of any cardiovascular fitness changes obtained through the exercise program; (4) evaluation of betaendorphin, ACTH, and cortisol levels; and (5) evaluation of other types of aerobic exercise for use with this patient population.

References

[1] Wolfe F, Smythe H, Yunus J, et al. The American College of Rheumatology 1990 criteria for the classification of fibromyalgia. Arthritis Rheum. 1990;33:160-172. [2] Bennett R, Clark S, Goldberg L, et al. Beyond fibromyalgia: ideas on etiology and treatment. J Rheumatol. 1989;16(suppl 19):185-191. [3] Goldenberg D. Fibromyalgia syndrome. JAMA. 1987;257:2782-2787. [4] Goldenberg D, Felson D, Dinerman H. A randomized, controlled trial of amitriptyline and naproxen in the treatment of fibromyalgia. Arthritis Rheum. 1986;29:1371-1377 [5] Mazanec D. First year of a rheumatologist in private practice. Arthritis Rheum. 1982;25:718-719. [6] Goldenberg D. High frequency of fibromyalgia in patients with chronic fatigue seen in a primary care practice. Arthritis Rheum. 1990;33: 381-387. [7] Shore M, McFarlane C. Cyclobenzaprine: a novel centrally acting skeletal muscle relaxant. Neuropharmacology. 1975;14:675-684. [8] McCain G. Role of physical fitness training in the fibrositis/fibromyalgia syndrome. Am J Med. 1986;81(suppl 3A):73-77. [9] McCain G, Bell D, Mai F, Halliday P. A controlled study of the effects of a supervised cardiovascular fitness training program on the manifestations of primary fibromyalgia. Arthritisr Rheum. 1988;31:1135-1141. [10] Paulev P, Thorboll J, Neilsen, U, et al. Opioid involvement in the perception of pain due to endurance exercise in trained man, Jpn J Physiol. 1989;39:67-74. [11] Janal M, Colt E, Clark W, Glusman M. Pain sensitivity, mood, and plasma endocrine levels in man following long-distance running: effects of naloxone. Pain. 1984;19:13-25. [12] Gun J. Relief of common migraine by exercise. J Neurol Neurosurg Psychiatry. 1987;50: 1700-1701. [13] Ekdahl C, Ekman R, Andersson S, et al. Dynamic training and circulating levels of corticotropin-releasing factor, beta-lipotropin, and beta-endorphin in rheumatoid arthritis. Pain. 1990;40:35-42. [14] McCain G. Nonmedicinal treatments in primary fibromyalgia. Rheum Dis Clin North Am. 1989; 15:73-90. [15] Howlett T. Hormonal responses to exercise and training: a short review. Clin Endocrinol. 1987;26:723-742. [16] Bennett R, Beyond fibromyalgia: ideas on etiology and treatment, J Rheumatol. 1989; 16(suppl 19)185-191. [17] Bengtsson A, Henriksson K. The muscle in fibromyalgia: a review of Swedish studies. J Rheumatol. 1989;16(suppl 19):144-149. [18] Klug GA, McAuley E, Clark S. Factors influencing the development and maintenance of aerobic fitness: lessons applicable to the fibrositis syndrome. J Rheumatol. 1989; 16 (suppl 19):30-39. [19] American College of Sports Medicine. Guidelines for Exercise Testing and Prescription, 4th ed. Philadelphia, Pa: Lea & Febiger; 1991. [20] Derogatis L, Melisaratos N. The brief symptom inventory: an introductory report. Psychol Med 1983;13:595-605. [21] Bergner M, Bobbitt R, Pollard W, et al. The sickness impact profile: validation of a health status measure. Med Carg. 1976;14:57-67. [22] Melzack R. The McGill pain questionnaire: major properties and scoring methods. Pain. 1975;1:277. [23] Follick M, Smith T, Ahern D. The sickness impact profile: global measure of disability in chronic low back pain. Pain. 1985;21:67-76. [24] McArdle W, Katch F, Katch V. Exercise Physiology. 3rd ed. Philadelphia, Pa: Lea & Febiger; 1991.

DS Nichols, PhD, PT, is Assistant Professor, Physical Therapy Division, School of Allied Medical Professions, The Ohio State University, 1583 Perry St, Columbus, OH 43210-1234 (USA), Address all correspondence to Dr Nichols.

TM Glenn, PhD, PT, is Assistant Professor, Physical Therapy Division, School of Allied Medical Pro The Ohio State University.

The study protocol was approved by The Ohio State University Biomedical Sciences Human Subject Review Committee.

This article was submitted March 29, 1993, and was accepted December 7, 1993.