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Keywords:

  • intermittent claudication;
  • weight loss;
  • incidence;
  • recovery;
  • obesity surgery

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Objective: To compare the prevalence of effort-related calf pain in an obese and a general population and to analyze the incidence of and recovery from such pain after surgical and conventional obesity treatment.

Research Methods and Procedures: A random sample of 1135 subjects from a general population was compared with 6328 obese subjects in the Swedish Obese Subjects study. Obese subjects were followed longitudinally, and information about calf pain was obtained from surgically and conventionally treated patients for up to 6 years.

Results: In both sexes, self-reported calf pain was more common in the obese than in the general population [odds ratios (ORs) 5.0 and 4.0 in men and women, respectively, p < 0.001]. Obese patients undergoing surgery had a lower 6-year incidence of calf pain compared with the conventionally treated control group (ORs 0.39 and 0.61, p < 0.05). Among subjects reporting symptoms at baseline, the 6-year recovery rate was higher in the surgical group compared with the control group (ORs 15.3 and 5.9, p < 0.001).

Discussion: Obese subjects have markedly more problems with effort-related calf pain than the general population. Surgical obesity treatment reduces the long-term risk of developing claudication symptoms and increases the likelihood of recovering from such symptoms.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Intermittent claudication is a common clinical symptom and is most often due to peripheral atherosclerotic vascular disease. Risk factors for vascular claudication are largely the same as those for atherosclerosis and include smoking, diabetes, hypertension, and dyslipidemia (1). Apart from restricting mobility and interfering with the patient's lifestyle, intermittent claudication is associated with an increased risk of morbidity and mortality from coronary heart disease and cerebrovascular disease (2, 3, 4).

Symptoms of intermittent claudication are, however, not due solely to peripheral atherosclerotic disease. Spinal stenosis, degenerative arthritis in the lower extremities, and venous insufficiency are examples of other conditions that may give rise to effort-related pain in the lower extremities (5).

Obesity is associated with a cluster of cardiovascular risk factors (6) and an increased risk of myocardial infarction (7) and stroke (8). Furthermore, obesity exerts a mechanical load on the lower body and is associated with an increased frequency of low back pain (9, 10), osteoarthritis of the knee (11), and varicose veins (12). However, data on exercise-induced calf pain in the obese population are scarce, and the possible effect of weight loss on such symptoms has not been investigated.

The aim of this study was to compare the prevalence of self-reported, effort-related calf pain in an obese and a general population and to study changes in the incidence of and recovery from such pain after bariatric surgery.

Research Methods and Procedures

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Swedish Obese Subjects (SOS)1 Study

The SOS study is an ongoing nationwide research project that started in 1987 with the primary aim of determining whether morbidity and mortality rates among the obese can be reduced by intentional weight reduction (13). The SOS study consists of three parts; a cross-sectional registry study of 6328 obese subjects, a longitudinal controlled intervention study of 4047 obese subjects, and a cross-sectional reference study of 1135 randomly selected subjects from a general population.

The registry study is basically an extensive health examination designed to characterize obese subjects in terms of genetics, medical history, metabolic aberrations, body fat distribution, food habits, and psychological and socioeconomic variables. The registry study also serves as a recruitment base for the subsequent intervention study.

In the intervention study, 2010 surgically treated obese patients are compared with a control group of 2037 matched obese patients receiving conventional treatment in primary health care. The obese controls are offered treatment according to the customary regime at each participating health care center, and no attempt is made to standardize their management. Follow-up is performed at regular outpatient visits, and self-administered questionnaires are dispatched 6 months, 1, 2, 3, 4, 6, 8, 10, 15, and 20 years after inclusion. The inclusion of patients in the intervention study was completed in January 2001. The inclusion criteria were age 37 to 60 years and BMI ≥ 34 kg/m2 for men and ≥38 kg/m2 for women.

Patients in the SOS registry study who were interested in surgery and met the inclusion criteria but not the exclusion criteria for the intervention study were invited to discuss bariatric surgery with a surgeon. Subjects who subsequently accepted an operation form the surgical group. The permitted operations were gastric banding, vertical banded gastroplasty, or gastric bypass, according to local practice at the 25 collaborating surgical departments. The conventionally treated control group was selected from eligible patients in the registry study by a computerized matching procedure, taking account of gender and 18 matching variables (13, 14). Patients in the conventionally treated group received the same treatment as obese patients generally do at the 480 collaborating primary health care centers, including dietary advice, behavior modification, very-low-caloric diet, physical training, or pharmaceutical treatment, according to local practice.

The SOS reference study is a population study conducted between 1994 and 1999 (15). A random sample of 2037 men and women 37 to 60 years old was selected from the population registry, and 1135 agreed to participate. They were examined with the same questionnaires and health examination as participants in the SOS registry study. Follow-up examinations are planned after 10, 15, and 20 years. The ethics committees at all Swedish medical faculties have approved the SOS and SOS reference studies, and informed consent was obtained from all subjects.

Study Populations

In the cross-sectional part of the present study, we used information on all 6328 patients in the SOS registry study and the 1135 SOS reference subjects. In the longitudinal part of the present study, the 1879 conventionally treated patients and the 1854 patients undergoing surgery who were included before October 31, 1999 form the study group for analyses of 2-year changes. Of these, 348 controls (18.5%) and 156 patients undergoing surgery (8.4%) were lost to follow-up. Only subjects who completed the 2-year examination were used in the analyses.

For the 6-year follow-up, the 1235 controls and 1312 patients undergoing surgery who were included before October 31, 1995 were used. After 6 years, 29.3% and 20.5% in the control and surgical group, respectively, were lost to follow-up, leaving 873 and 1043 subjects with complete 6-year data.

Measurements and Questionnaires

Body weight was measured to the nearest 0.1 kg and height to the nearest 0.01 m. BMI was calculated as weight divided by height squared (kilograms per meter squared).

Information about effort-related calf pain was collected through self-administered questionnaires modified from Rose et al. (16). In the cross-sectional study, the SOS registry and SOS reference subjects completed the questionnaires once. Patients in the longitudinal intervention study answered the questions at inclusion and again after 0.5, 1, 2, 3, 4, and 6 years. The questions used were formulated as:

A: Do you usually suffer from pain in your calves when walking uphill, upstairs or on flat ground? Yes/No.

B: Does the pain disappear if you stop walking? Yes/No.

C: If the pain disappears when you stop walking, how soon? Within 5 minutes/after more than 5 minutes.

Subjects who responded yes to questions A and B and within 5 minutes to question C were classified as having effort-related calf pain. In the longitudinal analyses, subjects reporting symptoms at least once during the given follow-up period were defined as cases.

Information on smoking habits, leisure time physical activity, current working status, and work-restricting pain in knee and ankle joints was obtained from self-administered questionnaires. The physical activity level was coded as sedentary, moderate, or regular. Subjects reporting no working hours during a week due to early retirement or sick leave were classified as “not working.”

Statistics

In the cross-sectional part of the study, the gender-specific prevalence of effort-related calf pain was analyzed using a logistic regression model, adjusting for age, smoking, working status, physical activity, and knee/ankle pain. We report odds ratios (ORs) with 95% confidence intervals (CIs). To study the relationship between BMI and the prevalence of calf pain, the SOS and SOS reference groups were divided into gender-specific BMI tertiles.

In the longitudinal analyses, gender-specific incidence rates were compared between the two treatment groups using logistic regression models, adjusting for baseline differences in age, smoking, working status, physical activity levels, and knee/ankle pain. Similarly, recovery rates among those who reported symptoms at baseline were compared using a logistic regression model. ORs and 95% CIs are reported. All of the analyses were performed using the Stata statistics package (StataCorp, College Station, TX).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Cross-Sectional Comparison

Gender-specific characteristics of the SOS registry and SOS reference populations used in the cross-sectional analysis are shown in Table 1. Subjects in the SOS registry study were markedly heavier than subjects in the SOS reference study. The percentage of subjects not working regularly was higher among the obese subjects, and they also had a more sedentary lifestyle. The prevalence of work-restricting pain in the knee or ankle joints was markedly higher in the obese.

Table 1.  Baseline characteristics of subjects in the SOS registry and SOS reference studies (mean and SD are shown)
 
SOSRegistryReferencepRegistryReferencep
Number of subjects (n)2460524 3868611 
Age (years)47.6 (5.9)49.8 (7.0)<0.00147.3 (6.1)49.3 (7.0)<0.001
Height (m)1.78 (0.07)1.79 (0.07)0.0031.65 (0.06)1.66 (0.06)<0.001
Weight (kg)121.1 (16.3)83.3 (12.5)<0.001112.2 (13.9)68.0 (11.6)<0.001
BMI (kg/m2)38.0 (4.4)25.8 (3.4)<0.00141.3 (4.4)24.7 (4.1)<0.001
Not working (%)13.95.9<0.00119.94.9<0.001
Smokers (%)23.918.60.00822.522.41.000
Physical activity, leisure time  <0.001  <0.001
 Sedentary (%)35.110.2 39.111.5 
 Moderate (%)60.066.9 58.472.2 
 Regular (%)4.823.0 2.516.4 
Work-restricting pain      
 Knee or ankle (%)36.211.7<0.00144.79.8<0.001

The prevalences of effort-related calf pain were 22.7% and 26.8% in the obese men and women, respectively, as compared with 4.4% and 6.8% among the reference men and women (Table 2). ORs for having calf pain, adjusted for age, smoking, working status, physical activity, and work-restricting pain in knee/ankle joints, were 5.0 and 4.0 in obese men and women, respectively, as compared with the reference subjects (p < 0.001 for both comparisons).

Table 2.  Prevalence of effort-related calf pain in the SOS registry and SOS reference studies
 
SOSRegistryReferencep*RegistryReferencep*
  • *

    Fisher's exact test.

  • Adjusted for age, smoking, working status, physical activity, and work-restricting pain in knee/ankle joints.

Number of subjects (n)2460524 3868611 
Claudication symptoms (%)22.74.4<0.00126.86.8<0.001
Odds ratio (95% CI)5.0 (3.2–7.8)  4.0 (2.8–5.6)  

To relate the prevalence of effort-related calf pain to body weight, subjects in the SOS reference and SOS registry studies were divided into tertiles of BMI (Figure 1). Among women in the reference study, the prevalence of calf pain increased with increasing BMI, but in obese women in the registry study, symptoms decreased as BMI became higher. Among men in the reference and registry studies, the prevalence of calf pain increased with increasing BMI, but this was not statistically significant.

image

Figure 1. Prevalence of effort-related calf pain by BMI in the SOS registry and SOS reference studies. The first tertile is used as the reference group. ORs (95% CIs) are adjusted for age, BMI, smoking, working status, physical activity, and work-restricting pain in knee/ankle joints.

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Longitudinal Comparison

The baseline characteristics of the obese subjects included in the longitudinal part of the present study are shown in Table 3. Surgically treated subjects completing the 2-year follow-up were heavier at baseline than conventionally treated controls. The percentage of subjects not working was similar in both groups, whereas patients undergoing surgery had a more sedentary lifestyle. Subjects in the surgically treated group reported more work-restricting pain in the knee or ankle joints. Effort-related calf pain at baseline was slightly more frequent in the surgically treated group. The surgically treated group had markedly larger weight reductions after both 2 and 6 years.

Table 3.  Baseline characteristics and weight change in patients undergoing surgery and conventionally treated patients who completed the 2-year follow-up in the SOS intervention study. (The mean and standard deviation are shown.)
 
TreatmentSurgicalConventionalpSurgicalConventionalp
Number of subjects495450 12031081 
Age (years)47.4 (5.7)48.5 (6.0)0.00647.5 (6.0)48.7 (6.2)<0.001
Height (m)1.79 (0.06)1.80 (0.07)0.1411.64 (0.06)1.65 (0.06)0.222
Weight (kg)132.0 (16.7)125.5 (16.5)<0.001115.5 (13.3)110.5 (14.4)<0.001
BMI (kg/m2)41.1 (4.6)38.8 (4.7)<0.00142.7 (4.1)40.7 (4.4)<0.001
Not working (%)15.617.30.48221.017.70.044
Smokers (%)24.623.00.59224.019.50.011
Physical activity, leisure time  <0.001  <0.001
 Sedentary (%)41.429.5 48.034.4 
 Moderate (%)53.462.7 49.762.0 
 Regular (%)5.37.8 2.33.6 
Work-restricting pain      
 Knee or ankle (%)43.125.9<0.00146.734.2<0.001
Calf pain on exertion (%)20.616.40.11228.620.1<0.001
Weight change (kg) over      
 2 years (kg)−29.5 (15.1)−0.4 (9.6)<0.001−27.6 (13.7)−0.3 (8.5)<0.001
 6 years (n)305284 738589 
 6 years (kg)−22.8 (15.1)1.0 (12.7)<0.001−19.7 (14.2)1.3 (10.1)<0.001

Among men and women with no calf pain at baseline, the risk of developing these symptoms during both the 2- and 6-year follow-ups was significantly lower in the surgically treated group compared with the control group (adjusted ORs for surgically treated group vs. controls ranging from 0.39 to 0.61) (Table 4).

Table 4.  Incidence of effort-related calf pain in patients undergoing surgery and conventionally treated patients in the SOS intervention study
    
Incidence (%)SurgicalConventionalp*Odds ratio95% CI
  • *

    Fisher's exact test.

  • Adjusted for age, BMI, smoking, working status, physical activity and work-restricting pain in knee/ankle joints.

Men     
 2-year8.913.30.0650.50(0.30–0.81)
 6-year12.820.90.0200.39(0.23–0.68)
Women     
 2-year8.213.3<0.0010.50(0.36–0.69)
 6-year14.120.10.0140.61(0.43–0.88)

Similarly, the recovery rates among subjects reporting calf pain at baseline were markedly improved in the surgically treated group when compared with the control group. The relative odds for being without symptoms during the 2- and 6-year follow-ups, surgically treated group vs. controls, varied from 5.9 to 15.3 (Table 5).

Table 5.  Recovery from effort-related calf pain in patients undergoing surgery and conventionally treated patients in the SOS intervention study
    
Recovery (%)SurgicalConventionalp*Odds ratio95% CI
  • *

    Fisher's exact test.

  • Adjusted for age, BMI, smoking, working status, physical activity, and work-restricting pain in knee/ankle joints.

Men     
 2-year73.529.7<0.0018.5(3.9–18.4)
 6-year62.916.7<0.00115.3(5.0–47.1)
Women     
 2-year72.130.4<0.0016.8(4.5–10.2)
 6-year58.723.2<0.0015.9(3.3–10.4)

After pooling data from the control and surgically treated groups, the 2- and 6-year incidences and recovery rates were related to the degree of weight change. There was a clear dose-response association between the risk of claudication symptoms and the degree of weight loss for both the incidence and recovery measures (Figures 2 and 3).

image

Figure 2. Incidence of effort-related calf pain by weight change in the SOS intervention study. The group with a weight loss > 20% is used as the reference group. ORs (95% CIs) are adjusted for age, BMI, smoking, working status, physical activity, and work-restricting pain in knee/ankle joints at baseline.

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image

Figure 3. Recovery from effort-related calf pain by weight change in the SOS intervention study. The group with a weight loss > 20% is used as the reference group. ORs (95% CIs) are adjusted for age, BMI, smoking, working status, physical activity, and work-restricting pain in knee/ankle joints at baseline.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

The present study demonstrates that obese people experience markedly more pain in the calf on exertion than the general population. Surgically induced weight loss reduces the long-term risk of developing calf pain during exercise and increases the likelihood of recovering from such symptoms.

The high prevalence of calf pain on exertion among participants in the SOS study has been reported previously (13) and contrasts to some degree with other epidemiological studies applying similar diagnostic questionnaires. In those studies, the association between BMI and intermittent claudication was found to be weak (17) or nonexistent (18, 19). In one study, however, intermittent claudication was related to central body fat distribution (20). The difference is difficult to explain, but previous trials did not study the obese population specifically, and high proportion of smokers, who tend to be lean, could have blunted the effect of fatness.

The underlying causes of exercise-induced calf pain reported by obese patients in the present study are not clear, but it is possible that both vascular and nonvascular mechanisms are involved. The relatively young age of our study group and the high prevalence of symptoms among obese females are not typical of atherosclerotic occlusive disease. Despite this, obese patients display increased frequencies of diabetes, hypertension, and dyslipidemia, and these cardiovascular risk factors have been related to endothelial dysfunction (21). In accordance, obese patients have been found to have impaired systemic vasodilatation (22) and deficient muscle and skin microcirculation (23) when exposed to mental stress. Furthermore, obesity in middle-aged people of both sexes predicts premature carotid artery atherosclerosis (24), coronary heart disease (25), and cerebrovascular disease (8, 26).

Obesity not only contributes to inadequate vasodilator responses and premature atherosclerosis but also exerts an increased work load on the lower extremities, leading to higher muscle cell oxygen consumption on ambulation. The combination of increased work load and deficient vasodilatation could predispose to an imbalance between muscle oxygen demand and supply and result in early calf muscle ischemia. A mismatch between muscle perfusion and metabolic needs would also be expected to improve after weight loss, which is in line with the high recovery rate among patients treated with bariatric surgery. Support for the importance of body mass with respect to leg ischemia is found in a study by Wyatt et al. (27), in which patients with claudication experienced increased symptoms and a reduced walking distance when carrying weights.

Obesity carries an increased risk of low back pain (9, 10), and, because pain from the lower lumbar region is occasionally referred to the calf, this may produce symptoms of intermittent claudication. Radiographic studies have shown that obese patients have a high frequency of lumbar spine degenerative changes (28), but the prevalence of true spinal stenosis among the obese is unknown. There are, however, some interesting case reports on lumbar epidural lipomatosis in obese patients exerting mechanical pressure on the nerve roots and giving rise to neurogenic claudication (29). In such patients, a regression of excess epidural fat and an improvement in symptoms has been demonstrated after weight loss (30).

A high body weight exerts increased forces on joints of the lower extremities, and obesity has been shown to be associated with degenerative arthritis in the hip, knee, and ankle (11, 28). Furthermore, weight loss has been shown to reduce the risk of pain in these joints (10, 28, 31). Lower extremity osteoarthritis, especially in the knee and ankle, may give rise to pain in the calf on ambulation and may, therefore, be reported by patients as claudication. In the statistical analysis, therefore, we adjusted for work-restricting pain in the knee and ankle joints. This did not, however, affect the association between obesity and symptoms of exercise-induced calf pain.

Chronic venous insufficiency is often associated with symptoms of heaviness, tension, or aching in the leg after prolonged standing. Occasionally, with lower extremity exercise, patients experience aggravated symptoms which are thought to be due to a rapid increase in superficial and deep venous pressure. These symptoms have been referred to as venous claudication. Obesity has been found to be a risk factor for varicose veins in women (32), and this might, to some extent, explain the high prevalence of self-reported calf pain among obese women in the present study.

Regardless of etiology, effort-related calf pain limits exercise capacity and, therefore, may be responsible, in part, for the high prevalence of sedentary behavior observed among obese patients. This is of significance because physical inactivity not only contributes to further weight gain but is also associated with increased cardiovascular morbidity and mortality (33, 34). Self-reported symptoms of intermittent calf pain tended to increase with the degree of obesity in men but not in women. This might indicate that there is a gender difference with respect to underlying cause or that mobility among severely obese women is so restricted that they do not experience symptoms.

The improvement of symptoms was related to the degree of weight loss and to this loss being maintained over a follow-up period of 6 years. Surgical obesity treatment has been shown to promote increased leisure-time physical activity (35), and recovery from exercise-induced leg pain is likely to contribute to this positive effect. Enhanced physical activity is of great importance because it promotes general well-being and reduces cardiovascular risks (36).

One limitation of the present study is that the identification of effort-related calf pain was based merely on self-reported subjective symptoms. During the study period, noninvasive testing to verify the presence or absence of significant leg ischemia was not available. The underlying causes of the high prevalence of calf pain on ambulation among obese subjects, therefore, remain speculative. On the other hand, the strengths of the study are the use of both cross-sectional and longitudinal data that relate to a large patient cohort and cover a wide range of BMI. Furthermore, all of the subjects were examined using the same standardized techniques, and both treatment groups received similar care during follow-up.

Self-reported symptoms of intermittent calf pain in the obese seem to be a dynamic phenomenon and seem to be related to the degree of obesity, at least in men. Whether the cause might be a mismatch between perfusion and metabolic needs in the leg muscle or a result of mechanical load on the musculoskeletal and/or venous systems is not clear. Regardless of etiology, surgical obesity treatment reduces the long-term risk of developing calf pain on exertion and increases the likelihood of recovering from such symptoms. As a result, when evaluating patients with symptoms of exercise-induced leg pain, obesity should be taken into account and weight reduction considered as part of management.

Acknowledgment

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

The SOS study was supported by the Swedish Research Council (Grant 05239) and by F. Hoffmann-La Roche Ltd.

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  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References
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