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Clinical Investigations: EXERCISE |

The 6-min Walk Test*: A Quick Measure of Functional Status in Elderly Adults FREE TO VIEW

Paul L. Enright, MD; Mary Ann McBurnie, PhD; Vera Bittner, MD; Russell P. Tracy, PhD; Robert McNamara, MD; Alice Arnold, PhD; Anne B. Newman, MD; for the Cardiovascular Health Study
Author and Funding Information

*From the University of Alabama at Birmingham (Dr. Bittner), Birmingham, AL; PAD Clinical Trial Center (Dr. McBurnie), Seattle, WA; Pediatrics (Dr. Newman), University of Pittsburgh, Pittsburgh, PA; University of Vermont (Dr. Tracy); University of Arizona (Dr. Enright) and private practice (Dr. McNamara), Phoenix, AZ; University of Washington Coordinating Center (Dr. Arnold), Seattle, WA.

Correspondence to: Paul Enright, MD, 4460 East Ina Rd, Tucson, AZ 85718; e-mail: lungguy@aol.com


*From the University of Alabama at Birmingham (Dr. Bittner), Birmingham, AL; PAD Clinical Trial Center (Dr. McBurnie), Seattle, WA; Pediatrics (Dr. Newman), University of Pittsburgh, Pittsburgh, PA; University of Vermont (Dr. Tracy); University of Arizona (Dr. Enright) and private practice (Dr. McNamara), Phoenix, AZ; University of Washington Coordinating Center (Dr. Arnold), Seattle, WA.


Chest. 2003;123(2):387-398. doi:10.1378/chest.123.2.387
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Published online

Objectives: To determine the correlates of the total 6-min walk distance (6MWD) in a population sample of adults ≥ 68 years old.

Methods: The standardized 6-min walk test (6MWT) was administered to the Cardiovascular Health Study cohort during their seventh annual examination.

Results: Of the 3,333 participants with a clinic visit, 2,281 subjects (68%) performed the 6MWT. There were no untoward events. The mean 6MWD was 344 m (SD, 88 m). Independent general correlates of a shorter 6MWD in linear regression models in women and men included the following: older age, higher weight, larger waist, weaker grip strength, symptoms of depression, and decreased mental status. Independent disease or risk factor correlates of a shorter 6MWD included the following: a low ankle BP, use of angiotensin-converting enzyme inhibitors, and arthritis in men and women; higher C-reactive protein, diastolic hypertension, and lower FEV1 in women; and the use of digitalis in men. Approximately 30% of the variance in 6MWD was explained by the linear regression models. Newly described bivariate associations of a shorter 6MWD included impaired activities of daily living; self-reported poor health; less education; nonwhite race; a history of coronary heart disease, transient ischemic attacks, stroke, or diabetes; and higher levels of C-reactive protein, fibrinogen, or WBC count.

Conclusions: Most community-dwelling elderly persons can quickly and safely perform this functional status test in the outpatient clinic setting. The test may be used clinically to measure the impact of multiple comorbidities, including cardiovascular disease, lung disease, arthritis, diabetes, and cognitive dysfunction and depression, on exercise capacity and endurance in older adults. Expected values should be adjusted for the patient’s age, gender, height, and weight.

Figures in this Article

The ability to walk for a distance is a quick and inexpensive performance-based measure, and an important component of quality of life, since it reflects the capacity to undertake day-to-day activities or, conversely, functional limitation.1The 6-min walk test (6MWT) can be performed by many elderly, frail, and severely limited patients who cannot be tested using standard (and more expensive) maximal cycle ergometry or treadmill exercise tests.2Walking tests are more reliable than other performance-based measures in elderly persons, such as timed chair stands and weight lifting.3The 6-min walk distance (6MWD) is known to be reduced by several types of diseases, including obstructive lung disease, heart failure, arthritis, and neuromuscular disease.45

Previous studies using the 6MWT were limited to patients with a given disease, and did not include elderly persons from several community samples. The Cardiovascular Health Study (CHS) is a prospective observational study of a general population sample designed to study the epidemiology and risk factors associated with cardiovascular disease (CVD) in the elderly. The correlates of four performance-based measures—gait speed, timed chair stands, grip strength, and maximal inspiratory pressure—obtained during the baseline examination of the cohort have previously been described.6 The standardized 6MWT was included in a follow-up examination of the cohort, along with many tests of cardiovascular and pulmonary risk factors and disease. We hypothesized that the 6MWD would be associated with many of these factors.

Study Population

Participants in the CHS were selected using a Medicare eligibility list provided by the US Health Care Financing Administration for the four participating communities: Forsyth County, North Carolina; Pittsburgh, PA; Sacramento County, California; and Washington County, Maryland. These communities are diverse in proportion of minorities, education and income levels, degree of urbanization, death rates, and availability of medical care. The initial study cohort of 5,201 participants was recruited and examined in 1989 through 1990. An additional cohort of 687 African Americans was enrolled in 1992 and 1993 in order to enhance the representation of the study. The 6MWT was done just once, during the seventh annual clinic examination of the original cohort and the fourth annual examination of the added cohort (June 1996 to May 1997).

The following were exclusion factors for study entry: institutionalized, terminal illness; inability to walk, communicate, or give informed consent; or likely to move from the area during the next 3 years. Enrolled CHS participants were younger, more educated, and more likely to be married and white than those who refused or were ineligible. The CHS design and recruitment are described in detail elsewhere.78 The research protocol was reviewed and approved by the institutional review board for human studies at the four clinical centers, and informed consent was obtained.

Examinations

Study participants completed standardized interviews in both the home and the field center, and extensive examinations at the field centers at baseline and during the annual examinations. Not all components were repeated at each annual visit. Standing height was measured in stocking feet to the nearest centimeter using a stadiometer, and weight was measured using a balance beam scale, recalibrated monthly. Handgrip strength was measured using a Jamar dynamometer set at the second handle position. The participants were seated with their wrist in a neutral position and elbow flexed 90°. Grip strength was measured three times for each hand, and the highest value (in kilograms) from the participant’s dominant hand was used for our analysis. A medication inventory was obtained at each examination,9 but the specific indication for each medication was not determined.

Participants assessed their general health by answering the question, “Would you say, in general, your health is (excellent, very good, good, fair, or poor)?” Limitation of instrumental activities of daily living (ADL) was defined as trouble performing any of the following: light or heavy housework, shopping, meal preparation, money management, and using the telephone. Symptoms of depression were assessed using the modified Center for Epidemiologic Studies depression scale of 0 to 30.10The categorical variable depression (a mood, not a diagnostic category) was defined as a score of ≥ 15. Good social support was defined as a score of ≥ 12 using a standard scale.11 Cognitive function was assessed by trained interviewers using a modified Mini-Mental Status Examination (MMSE),12 scored on a scale of 0 to 100 (including both serial 7s and spelling “world” backwards). All of the measurements described thus far were concurrent with the examination in which the 6MWT was done.

From 1992 through 1993, we measured each subject’s systolic BP in both ankles (tibial arteries) and their right arm (brachial artery) at rest in supine position, using a hand-held Doppler transducer, and later calculated the ankle-arm index (AAI), a sensitive subclinical measure of reduced blood flow to the legs.13Blood was obtained while fasting, and analyzed for RBC and WBC counts, blood chemistry, and lipoprotein levels.14At baseline for each cohort, blood was analyzed for C-reactive protein levels.15Echocardiography was performed during visits from 1995 through 1996.16

CVD Assessment

Health status was assessed at baseline through self-report of physician diagnosis of diseases. Self-report of CVDs were validated according to standardized criteria by the medications used, and by examination data such as BP, ECG,17echocardiography, and carotid ultrasound.18Cardiovascular events occurring after baseline and prior to the 6MWT were validated by a review of medical records and adjudicated according to standardized criteria.19

Pulmonary Assessments

Spirometry was performed according to American Thoracic Society (ATS) criteria,20with reference values previously obtained from healthy members of our cohort.21The smoking status of each participant at each examination was categorized as never-smoker, former smoker, or current smoker, using responses to the standardized ATS DLD-78 respiratory questionnaire.22

Exclusions from the 6MWT included the following: regular use of an ambulatory aid (cane or walker); a resting oxygen saturation < 90%; inability to walk due to musculoskeletal problems; chest pain in the previous 4 weeks; a heart attack, angioplasty, or heart surgery in the previous 3 months; heart rate < 50 beats/min at rest (unless a physician or nurse determined that an AV block or conduction problem was not the cause of the bradycardia); heart rate > 110 beats/min at rest; acute ST-T wave changes on the ECG; participant refusal; or judgment of the clinic staff that the participant would probably not be able to complete the walk safely (technician discretion). These exclusions were probably conservative (excluding many participants who would have eagerly and safely performed the test) because physicians could not be present in the clinics during all of the examinations to assess and treat symptomatic participants.

6MWT

The 6MWT was conducted according to a standardized protocol,23using an internal hallway with the 100-foot distance marked by colored tape on the floor. Participants were told that “the purpose of this test is to see how far you can walk in six minutes.” They were then instructed to “walk from end to end of the hallway at your own pace, in order to cover as much ground as possible.” Each minute, technicians encouraged the participants with the standardized statements “You’re doing well” or “Keep up the good work,” but were asked not to use other phrases. Participants were allowed to stop and rest during the test, but were instructed to resume walking as soon as they were able to do so. The technician used a mechanical lap counter to count the number of laps completed, and an electronic timer with a buzzer that sounded 6 min after the walk started. Before the walk started and at the end of the 6-min walk, participants were shown a modified Borg dyspnea scale24 printed on a card and asked to “indicate your current degree of shortness of breath” on a scale of “0 = nothing at all” to “10 = very, very severe.” At the end of the walk, they were asked if they had experienced any of the following specific symptoms: dyspnea, chest pain, light-headedness, or leg pain, or any other symptoms.

Statistical Methods

Preliminary descriptive analyses included frequencies, histograms, and error bar plots to examine bivariate relationships with total distance walked. For bivariate associations, Pearson χ2 tests were used to evaluate associations between categorical variables, analysis of variance F tests for associations between continuous and categorical variables, and t tests for partial correlations between continuous measures.

Multiple linear regression analysis was performed to determine relationships between total distance walked and potential predictors. Variables were examined for the linearity of their relationship with 6MWD using the additive and variance stabilizing transformation (AVAS) in S-Plus (StatSci; Seattle, WA).25 AVAS is a nonparametric regression technique that attempts to find smooth transformations that approximate an additive model. These transformations can be used to suggest appropriate functional forms for standard linear models. Linear piecewise transformations were suggested for AAI, diastolic BP (women only), and MMSE, as was a quadratic form for weight that was centered to reduce collinearity between the linear and quadratic terms. Median values appeared to be reasonable cut-points for the piecewise transformations. Analyses were stratified by gender based on results of preliminary analyses that suggested differences in some relationships by gender, but any variable that was entered into the model for one gender was also entered into the model for the other gender.

A series of stepwise regressions were fit for successive blocks of covariates. Candidate variables were stepped into the model in the following groups: demographics (age, race, site indicators, less than high school education); anthropometry (body mass index [BMI], waist circumference, weight, weight squared, standing height, and arm span); clinical and subclinical disease (prevalence for diabetes, arthritis, angina, congestive heart failure [CHF], claudication, myocardial infarction [MI], stroke, and transient ischemic attack [TIA], FEV1, AAI, diastolic and brachial and tibial systolic BP), measures of inflammation (fibrinogen, WBC count, and C-reactive protein); smoking status (current vs never or former); echocardiographic variables (left ventricular mass [LVM], regional wall motion, and percentage of fractional shortening); medications (β-blockers, diuretics, vasodilators, angiotensin-converting enzyme [ACE] inhibitors, calcium channel blockers, digitalis, hypertension, insulin, lipid-lowering, and nonsteroidal anti-inflammatory drugs for both genders; and estrogen in women); and “function” variables (grip strength, MMSE score, and depression score). To determine entry and removal of candidate variables from the model, p values of 0.05 and 0.06 were used, respectively. The piecewise terms were included in the model based on partial F tests for simultaneous significance of both coefficients. Once the stepwise selection was completed, the final models were refit using only the selected variables in order to minimize the amount of missing data. Appropriateness of the functional forms was reaffirmed using AVAS.

Adjustment was not made for multiple comparisons. All p values are presented as relative measures of the strength of the associations and should not be strictly interpreted because of the large number of statistical tests performed. Analyses were carried out using SPSS for Windows (Release 9.0; SPSS; Chicago, IL)26and S-Plus.27

Since the 6MWD was associated with age, gender, race, height, and weight, reference equations for the healthy subset of participants were determined using these variables as predictors of 6MWD in a linear regression model. Participants with factors associated with a shorter 6MWD were excluded from the healthy subset.

6MWT Exclusions and Safety

Of the 3,333 participants who attended the 1996 through 1997 clinic visit, approximately one third were excluded or chose not to try the 6MWT (Table 1 ). The 164 participants who started the walk but stopped walking before 6 min had elapsed (partial completers) were included in the analyses for this report. Those who completed the walk (n = 2,117) were significantly healthier in many respects when compared to the partial completers, or to those who did not perform the test (Table 2 ). Those with prevalent CVD (a history of angina, MI, CHF, claudication, TIA, or stroke) were much less likely to have tried or completed the walk. Half of the cohort who did not attend the clinic visit (and 37% of those who attended the clinic visit but did not try the walk) reported that their general health was only fair or poor, compared to only 16% of those who completed the walk.

There were no untoward events associated with the test (no need for emergency evaluation or therapy). All participants were asked about symptoms at the end of the walk, and approximately 75% said that they had no symptoms (Table 3 ). The most common symptoms reported by the others included leg pain, muscle or joint pain, discomfort, or fatigue. Only 29 participants reported chest pain. Thirty-nine percent of the 164 participants who were partial completers reported a symptom at that point (compared to 24% of those who walked for the entire 6 min); however, the distribution of symptoms did not differ between the two groups.

The mean distance walked was 362 m (1,188 feet) for men and 332 m (1,089 feet) for women. The 6MWD distribution was skewed toward shorter distances.

Bivariate and Nonlinear Associations With 6MWD

There was a nonlinear relationship of body weight and BMI with 6MWD (Fig 1 ). Patients with a low or a high weight (or BMI) did not walk as far as the others. The upper threshold for a lower distance was a BMI > 30 or a weight > 180 lb. We did not use BMI in subsequent models since it forces a specific relationship between weight and height that is less powerful as a predictor when compared to using both weight and weight squared in the model.

There was also a nonlinear association of ankle BP (and AAI) with 6MWD in both men and women (Fig 2 ). AVAS analysis suggested a breakpoint at an AAI of 1.1 in women and 1.2 in men. There was also a breakpoint (at 69 mm Hg) in the relationship of diastolic (brachial) BP and 6MWD in women (Fig 3 ).

For those variables that were significantly correlated with 6MWD, Table 4 lists their mean values for each quintile of 6MWD; for each categorical variable, the percentages are given. Disease and risk factors that were more likely in the lowest quintile of distance walked included a history of any CVD, diabetes, lower lung function, and weaker grip strength; and higher fibrinogen, C-reactive protein, and WBC count. Participants who reported limitations in ADL, fair to poor general health, more symptoms of depression, and those with lower cognitive function (lower MMSE score) did not walk as far. Although there was a tendency for those who did not walk as far to have abnormal echocardiographic findings, these trends were not significant.

Independent Predictors of 6MWD in Regression Models

Tables 5, 6 , show the independent correlates of 6MWD, using gender-specific, stepwise, linear regression models. Approximately 30% of the variance in 6MWD was explained by the final models. The distances were approximately 7% lower at two of the clinics (Hagerstown, MD, and Pittsburgh, PA). Age and waist size remained strongly associated with 6MWD. The nonlinear effects of weight and AAI also remained as strong predictors of 6MWD. Racial differences also persisted in the final models, but high school education became nonsignificant as disease variables entered the models. Diastolic BP, lung function, arthritis, and C-reactive protein level remained significant correlates in women.

The only echocardiographic variable that was significant in any model was moderate-to-severe left ventricular wall motion abnormalities in women (p = 0.002). Since only 776 women completed this examination, the overall strength of that model was decreased, and so we elected not to enter echocardiographic variables into the final models. None of the echocardiographic variables were significant in any of the models for men, but the use of digitalis and ACE inhibitors was associated with lower 6MWD, and the use of lipid-lowering medications was associated with a higher 6MWD.

In the final step of entering groups of variables into the models, three functional variables were significant: score on the MMSE, the depression symptom score, and grip strength. When they entered the models, race and education became much less important. Participants with better cognitive levels, fewer symptoms of depression, and a stronger grip strength walked farther.

The following factors were not independent correlates of the distance walked (p < 0.01) in the final models: educational level, height, current smoking, prevalent coronary heart disease (a history of MI, angina, CHF, stroke, or claudication), or the use of several cardiovascular medications (diuretics, antihypertensives, vasodilators, β-blockers, and calcium channel blockers), or nonsteroidal anti-inflammatory drugs, insulin, or estrogen by women.

Reference Equations for the 6MWD

Approximately one third of the 2,115 patients who completed the 6MWT remained in the healthy subset (Table 7 ). The 437 healthy women walked a mean of 367 m (confidence interval [CI], 249 to 479 m), and the 315 healthy men walked a mean of 400 m (CI, 280 to 532 m). The 71 healthy African-American participants walked an average of 40 m shorter distance than the others. The relationship of age with 6MWD was linear. There were no significant gender or race interaction terms with age, height, or weight in the model predicting 6MWD in the healthy subset. The total amount of variance in 6MWD explained by the model (R2) was only 20%. On average, the healthy 752 participants walked only 10.5% farther than the entire group who completed the test.

We found that most elderly persons can safely perform the 6MWT to quickly measure their functional status. We may be the first investigators to describe associations of 6MWD with impaired ADL; self-reported health; education; race; a history of coronary heart disease, TIA, stroke, or diabetes; and indexes of inflammation: (C-reactive protein, fibrinogen, and WBC count).

The 12-min walking test was introduced in 1968 as a guide to physical fitness,28and later applied to patients with COPD.29 It was then found that decreasing the time to 6 min did not significantly reduce the utility of the test.23 The 6MWT has been validated by high correlation with workloads, heart rate, oxygen saturation, and dyspnea responses when compared to standard bicycle ergometry and treadmill exercise tests in middle-aged adults3032 and in elderly persons.2,33

Anthropometric Correlates

Age, weight, and waist size were independently associated with the distance walked in this analysis, and these factors were also associated with gait speed and timed chair stands during their baseline examination.6 The gradual reduction of skeletal muscle mass and strength that generally occurs with aging3435 (and debilitating diseases that we did not measure) are probably responsible for the shorter distance walked by those > 85 years old. A taller height is associated with a longer stride, which makes walking more efficient, probably resulting in a longer distance walked in the taller men and women. After correcting for other factors, including height, elderly men did not walk farther than elderly women (in a model that included men and women together; data not shown).

Obesity increases the workload for a given amount of exercise, probably resulting in the shorter distance walked in participants with a higher body weight or BMI. On average, participants who were obese, as defined by a BMI > 30, walked approximately 85% of the distance completed by those of average body weight. Although BMI is a clinically useful index of obesity, exploratory analyses suggested that the specific functional form weight/height squared was not optimal for describing the relationship of weight and height with 6MWD. Waist size and body weight were more strongly associated with 6MWD than was BMI.

After correcting for age, gender, height, weight, and other confounders, elderly African-American women and men walked a shorter distance when compared to white men and women in our study. Investigators in Japan recently reported that the mean 6MWD of healthy elderly Japanese men and women36was similar to that reported for whites.3738

Cardiovascular Correlates

Participants who reported a history of any type of CVD (a history of angina, MI, heart failure, TIA, or stroke) did not walk as far as the others (Table 4). This was also true in the Tucson study.37 Men receiving ACE inhibitors and those receiving digitalis walked approximately 90% as far as others. This is probably because they were receiving these medications for heart failure,39which causes dyspnea on exertion, limiting exercise tolerance.40Approximately 42% of men and women who reported heart failure were receiving an ACE inhibitor, and one half were receiving digitalis. Use of these medications is probably an indicator of more clinically severe CHF; however, men receiving lipid-lowering medications walked approximately 7% farther than other men. Approximately 25% of men with a history of MI and 29% of those with claudication were receiving lipid-lowering medications. Although these medications act as markers of vascular disease, perhaps their use improves walking distance in such patients; a future study of these medications should investigate this possibility by including 6MWD as an outcome measure.41

In the bivariate analyses, there were only nonsignificant trends for participants with echocardiographic abnormalities to walk shorter distances, and only wall motion abnormalities in women were independently associated with 6MWD in the models. This lack of a relationship of echocardiographic variables with exercise ability was previously reported in patients with overt heart failure,42 perhaps because echocardiographic measurements are done while resting.

Both clinical and subclinical peripheral vascular disease (claudication and low AAI) were bivariately associated with substantially shorter 6MWD (Table 4). In the multivariate models, we used two terms for AAI (piecewise) since we found a breakpoint in the relationship between AAI and the 6MWD. The highest 6MWD was seen when the AAI was approximately 1.1 (Fig 3). 6MWD decreases as the AAI was higher or lower than 1.1. Previous studies of AAI suggest that a low AAI is associated with peripheral vascular disease,33 while a high AAI may be due to loss of arterial compliance.43

Pulmonary Correlates

We found that a lower FEV1 was a strong, independent predictor of a lower 6MWD in women. A low FEV1 is most commonly due to obstructive lung diseases such as COPD (due to decades of cigarette smoking) and asthma, but is also reduced in diseases that restrict lung volumes. Previous investigators have used the 6MWD as a measure of the severity of COPD and an outcome measure in COPD treatment studies.23,31,4445 We found that the FEV1 was also associated with gait speed and grip strength in the elderly women of this cohort.,6 Current smoking was bivariately associated with a significantly shorter distance walked in both studies, but in the gender-specific models, smoking status was replaced by indexes of subclinical diseases that are known to be caused by smoking.

Other Correlates

Previous studies using the 6-min walk have not included measures of symptoms of depression, mental status (MMSE), limitations of ADL, self-reported general health, or grip strength, all of which we found were independently associated with the 6MWD. A 1-U higher MMSE score was associated with walking 6 m farther in women, and a similar relationship was seen in men. The 7% lower mean 6MWD values found at two of the four clinics could be due to technicians at those clinics less frequently excluding frail participants, or giving less encouragement to walk farther (despite the attempt to standardize the messages); or it could be due to unmeasured differences in the populations in those communities.

Grip strength is a direct measure of skeletal muscle strength of the hands, but it is also an index of overall muscle strength, endurance, and disability.46It remained a strong, independent (linear) predictor of 6MWD in our models for both women and men. Mean grip strength was 23 kg for women and 40 kg for men in the 65-to 69-year age groups. For a 10-kg increment in grip strength, men and women walked an average of 14 m farther. A study from Finland demonstrated that muscle strength and walking speed can be increased substantially by physical exercise (either endurance or strength training) in elderly women.47

A limitation of this study is that one third of the participants were excluded from the walk, and they had generally poorer health than those who performed the test; however, their exclusion only decreased the power of the analyses to detect associations with these diseases. Those entered into the study, and those who came to the clinics for the examination between 1996 and 1997 (the only time the 6MWT was done) were survivors, and were healthier than older persons in institutions or hospitals.

Reference Equations for the 6MWD

The mean 6MWD in the healthy subset of participants was 367 m (CI, 249 to 479 m) for women, and 400 m (CI, 280 to 532 m) for men. Age, gender, race, height, and weight were all statistically significant predictors of 6MWD in the healthy subgroup, suggesting that these factors should be considered when comparing the 6MWD of an individual patient to healthy elderly persons; however, the reference equations obtained from this model explained only 20% of the variation in 6MWD. The fifth percentile of the 6MWD for the healthy participants, which may be considered the lower limit of the normal range, was approximately 75% of the predicted value (mean minus lower limit of the normal range: 400 m − 100 m = 300 m for men).

Our reference equation gives predicted (mean) 6MWDs that are substantially lower than those published by previous investigators.37,48 Our reference equations predicts distances of 430 m and 464 m for a 67-year-old white woman and man of average height and weight, respectively, while a study of 290 healthy adults in Tucson, AZ,37 predicts distances of 466 m and 544 m; the study of Rikli and Jones,48 which enrolled 7,183 older adults from 21 states, predicts distances approximately 50% greater than ours (624 m and 689 m, respectively, for the same woman and man).

Our choice of criteria for excluding participants from the healthy subgroup is probably not the reason for our lower distances, since we excluded more than two thirds of the cohort, yet the healthy subgroup only walked an average of 10.5% farther than the entire cohort who completed the test. The study of Rikli and Jones48 recruited participants using advertisements in newspapers, magazines, and journals (resulting in a recruitment bias toward highly fit individuals), while our participants were a community-based sample. The participants in the study by Rikli and Jones did 8 to 10 min of warm-up and stretching exercises before beginning the test, walked in groups of three to six outside on a rectangular track, and were instructed to “walk as fast as they comfortably could, trying to cover the maximum distance possible,” while our participants had no warm-up, walked alone, and were instructed to walk from end to end of the hallway at their own pace, in order to cover as much ground as possible.

Differences in participant recruitment and test instructions probably account for the lower distances walked by our participants when compared to the two other studies. The ATS has recently published detailed guidelines for 6MWT procedures49 that should be followed by investigators studying carefully selected healthy persons. This new document states that “a practice test is not needed in most clinical settings, but should be considered.” The CHS 6MWT done in 1996 was performed exactly according to the 2002 ATS guidelines, except that the instructions given to the CHS participants were to “walk from end to end of the hallway at your own pace, in order to cover as much ground as possible.” According to the new ATS guidelines, patients should be told to “Remember that the object is to walk as far as possible for six minutes, but don’t run or jog.” This seemingly small difference in the instructions may have caused the elderly CHS participants not to walk as quickly as they would have if the new ATS recommended instructions had been given to them.

The 6MWT should be useful for measuring changes in functional status (preintervention and postintervention) in the clinical setting, but considerable caution is needed when using currently available reference equations to determine if a given patient’s 6MWD is normal or low. According to the ATS review of previously published 6MWT studies, the increases due to the learning effect ranged from a mean of zero to 17%. Performance usually reaches a plateau after two tests done within a week. The reproducibility results from one study of 112 patients with stable, severe COPD suggest that an improvement of > 70 m in the 6MWD after an intervention is necessary to be 95% confident that the improvement was significant.50

In summary, most community-dwelling elderly persons can perform the 6MWT. Factors associated with a shorter distance walked are similar to those associated with a reduced oxygen uptake at maximal exercise reported by previous investigators. Unique factors measured by this study included cognitive function, symptoms of depression, limitations of ADL, indexes of inflammation, and the use of cardiovascular medications.

Participating Institutions and Principal Investigators

Wake Forest University School of Medicine, Gregory L. Burke, MD; ECG Reading Center, Wake Forest University, Pentti Rautaharju, MD, PhD; University of California, Davis, John Robbins, MD, MHS; The Johns Hopkins University, Linda P. Fried, MD, MPH; MRI Reading Center, The Johns Hopkins University, Nick Bryan, MD, PhD, and Norman J. Beauchamp, MD; University of Pittsburgh, Lewis H. Kuller, MD; Echocardiography Reading Center (baseline), University of California, Irvine, Julius M. Gardin, MD; Echocardiography Reading Center (follow-up), Georgetown Medical Center, John Gottdiener, MD; Ultrasound Reading Center, New England Medical Center, Boston, Daniel H. O’Leary, MD; Central Blood Analysis Laboratory, University of Vermont, Russell P. Tracy, PhD; Pulmonary Reading Center, University of Arizona, Tucson, Paul Enright, MD; Retinal Reading Center, University of Wisconsin, Ron Klein, MD; Coordinating Center, University of Washington, Richard A. Kronmal, PhD; and National Heart, Lung, and Blood Institute Project Office, Diane Bild, MD, MPH.

Abbreviations: 6MWD = 6-min walk distance; 6MWT = 6-min walk test; AAI = ankle-arm index; ACE = angiotensin-converting enzyme; ADL = activities of daily living; ATS = American Thoracic Society; AVAS = additive and variance stabilizing transformation; BMI = body mass index; CHF = congestive heart failure; CHS = Cardiovascular Health Study; CI = confidence interval; CVD = cardiovascular disease; LVM = left ventricular mass; MI = myocardial infarction; MMSE = Mini-Mental State Examination; TIA = transient ischemic attack

This research was supported by contracts N01-HC-85079 through N01-HC-85086, N01-HC-35129, and N01-HC-15103 from the National Heart, Lung, and Blood Institute.

Table Graphic Jump Location
Table 1. Participation, Exclusions, and Completion of the 6MWT
Table Graphic Jump Location
Table 2. Comparison of Study Participants Who Completed the 6MWT, Partial Completers, and Those Who Were Not Tested*
* 

Data are presented as mean (SD) or %.

 

This category includes participants who came into the clinic but refused the test, or were excluded from the test, or were unable to perform the test because of physical, cognitive, or equipment problems.

 

p values are unadjusted, and test for a trend across the categories (four rows).

Table Graphic Jump Location
Table 3. Symptoms Reported at the End of the 6MWT*
* 

Data are presented as No./total (%) or No. (%).

 

The majority of these symptoms involved muscle or joint pain, discomfort, or fatigue (n = 184). Other symptoms also included shortness of breath, tightness or pressure in chest, wheezing (n = 27); general weakness or fatigue (n = 26); dizziness or balance problems (n = 14); nausea (n = 6); and miscellaneous symptoms (n = 31). Some participants reported more than one symptom at the end of the test.

Figure Jump LinkFigure 1. The association of BMI by deciles with 6MWD. Note the shorter distance walked by obese elderly persons (BMI > 30).Grahic Jump Location
Figure Jump LinkFigure 2. The relationship between the AAI of systolic BP and 6MWD. A breakpoint was found at AAI of 1.10 for women and AAI of 1.20 for men.Grahic Jump Location
Figure Jump LinkFigure 3. The relationship of diastolic BP with 6MWD in elderly women. A breakpoint was found at a diastolic BP of 69 mm Hg.Grahic Jump Location
Table Graphic Jump Location
Table 4. Bivariate Associations With the Distance Walked During the 6MWT*
* 

Data are presented as mean (SD) or %. ln = natural log.

 

Unadjusted p values, testing for a trend across the quintiles of total distance walked.

 

Data are missing for these echocardiography variables from many subjects.

Table Graphic Jump Location
Table 5. Linear Regression Models Predicting 6MWD for Women (n = 1,094), With Same Variables in Model for Men and Women*
* 

See Table 4 for expansion of abbreviation.

Table Graphic Jump Location
Table 6. Linear Regression Models Predicting 6MWD for Men (n = 715), With Same Variables in Model for Men and Women*
* 

See Table 4 for expansion of abbreviation.

Table Graphic Jump Location
Table 7. Reference Equations for the 6MWD From the Healthy Subset of 437 Women and 315 Men
* 

Gender-specific cutpoints for obesity were > 90 kg for women and 101 kg for men, and for high waist size 118.5 cm for women and 116 cm for men.

Guralnik, J, Branch, L, Cummings, S, et al (1989) Physical performance measures in aging research.J Gerontol Med Sci44,M141-M146
 
Peeters, P, Mets, T The 6 minute walk as an appropriate exercise test in elderly patients with chronic heart failure.J Gerontol1996;51A,M147-M151
 
Jette, AM, Jette, DU, Ng, J, et al Are performance-based measures sufficiently reliable for use in multicenter trials?J Gerontol1999;54A,M3-M6
 
McGavin, CR, Artvinli, M, Naoe, H, et al Dyspnea, disability, and distance walked: comparison of estimates of exercise performance in respiratory disease.BMJ1978;2,241-243. [PubMed] [CrossRef]
 
Bittner, V, Weiner, DH, Yusuf, S, et al Prediction of mortality and morbidity with a six minute walk test in patients with left ventricular dysfunction.JAMA1993;270,1702-1707. [PubMed]
 
Hirsch, CH, Fried, LP, Harris, T, et al Correlates of performance-based measures of muscle function in the elderly: The Cardiovascular Health Study.J Gerontol1997;52A,M192-M200
 
Fried, LP, Borhani, NO, Enright, PL, et al The Cardiovascular Health Study: design and rationale.Ann Epidemiol1991;1,263-276. [PubMed]
 
Tell, GS, Fried, LP, Hermanson, B, et al Recruitment of adults 65 years and older as participants in the Cardiovascular Health Study.Ann Epidemiol1993;3,358-366. [PubMed]
 
Psaty, BM, Lee, M, Savage, PJ, et al Assessing the use of medications in the elderly: methods and initial experience in the Cardiovascular Health Study.J Clin Epidemiol1992;45,683-692. [PubMed]
 
Orme, J, Reis, J, Herz, E Factorial and discriminate validity of the CES-D scale.J Clin Psychol1986;42,28-33. [PubMed]
 
Cohen, S, Mermelstein, R, Kamarck, T, et al Measuring the functional components of social support. Saranson, IG Saranson, BR eds. Social support: theory, research and application. 1985; Martinus Nijhoff. Dordrecht, The Netherlands:.
 
Teng, EL, Chui, HC The modified Mini-Mental State (3MS) Examination.J Clin Psychol1987;48,314-318
 
Newman, AB, Siscovick, DS, Manolio, TA, et al Ankle-arm index as a marker of atherosclerosis in the Cardiovascular Health Study.Circulation1993;88,837-845. [PubMed]
 
Tracy, RP, Bovill, EG, Fried, LP, et al The distribution of coagulation factors VII and VIII and fibrinogen in adults over 65 years old: results for the Cardiovascular Health Study.Ann Epidemiol1992;2,509-519. [PubMed]
 
Tracy, RP, Lemaitre, R, Psaty, BM, et al Relationship of C-reactive protein to risk of cardiovascular disease in the Cardiovascular Health Study.Arterioscler Thromb Vasc Biol1997;17,1121-1127. [PubMed]
 
Gardin, JM, Wong, ND, Bommer, W, et al Echocardiographic design of a multicenter investigation of free-living elderly subjects: The Cardiovascular Health Study.J Am Soc Echocardiogr1992;5,63-72. [PubMed]
 
Furberg, CD, Manolio, TA, Psaty, BM, et al Major electrocardiographic abnormalities in persons aged 65 years and older: The Cardiovascular Health Study.Am J Cardiol1992;69,1329-1335. [PubMed]
 
O’Leary, DH, Polak, JF, Wolfson, SK, et al Use of sonography to evaluate carotid atherosclerosis in the elderly: Cardiovascular Health Study.Stroke1991;22,1155-1163. [PubMed]
 
Ives, DG, Fitzpatrick, AL, Bild, DE, et al Surveillance and ascertainment of cardiovascular events: The Cardiovascular Health Study.Ann Epidemiol1995;5,278-285. [PubMed]
 
American Thoracic Society. Standardization of spirometry, 1987 update.Am Rev Respir Dis1987;136,1285-1298. [PubMed]
 
Enright, PL, Kronmal, RA, Higgins, M, et al Spirometry reference values for women and men 65–85 years of age: Cardiovascular Health Study.Am Rev Respir Dis1993;147,125-133. [PubMed]
 
American Thoracic Society. Recommended respiratory disease questionnaires for use with adults and children in epidemiological research.Am Rev Respir Dis1978;6(part 2),7-23
 
Butland, RJA, Pang, J, Gross, ER, et al Two, six, and 12 minute walking tests in respiratory disease.BMJ1982;284,1607-1608. [PubMed]
 
Wilson, RC, Jones, PW A comparison of the visual analogue scale and modified Borg scale for the measurement of dyspnea during exercise.Clin Sci1989;76,277-282. [PubMed]
 
Tibshirani, R Estimating transformations for regression via additivity and variance stabilization.J Am Stat Assoc1988;83,394-405
 
Norusis, MJ. SPSS for Windows, base system user’s guide, release 9.0. 1998; SPSS. Chicago, IL:.
 
 S-Plus guide to statistical and mathematical analysis, version 3.2. 1993; StatSci. Seattle, WA:.
 
Cooper, KH A means of assessing maximal oxygen intake.JAMA1968;203,201-204. [PubMed]
 
McGavin, CR, Gupta, SP, McHardy, GJR Twelve minute walking test for assessing disability in chronic bronchitis.BMJ1976;1,822-823. [PubMed]
 
Langenfeld, H, Schneider, B, Grimm, W, et al The six minute walk test: an adequate exercise test for pacemaker patients?Pacing Clin Electrophysiol1990;13,1761-1765. [PubMed]
 
Spence, DPS, Hay, JG, Carter, J, et al Oxygen desaturation and breathlessness during corridor walking in COPD: effect of oxitropium bromide.Thorax1993;48,1145-1150. [PubMed]
 
Bernstein, ML, Despars, JA, Singh, NP, et al Re-analysis of the 12 minute walk in patients with COPD.Chest1994;105,163-167. [PubMed]
 
Montgomery, PS, Gardner, AW The clinical utility of a six minute walk test in peripheral arterial occlusive disease patients.J Am Geriatr Soc1998;46,706-711. [PubMed]
 
Fleg, JL, Lakatta, EG Role of muscle loss in the age-associated reduction in Vo2max.J Appl Physiol1988;65,1147-1151. [PubMed]
 
Tolep, K, Kelsen, SG Effect of aging on respiratory skeletal muscles.Clin Chest Med1993;3,363-378
 
Teramoto, S, Ohga, E, Ishii, T, et al Reference value of six-minute walking distance in healthy middle-aged and older subjects [letter].Eur Respir J2000;15,1132-1133. [PubMed]
 
Enright, PL, Sherrill, DL Reference equations for the six minute walk in healthy adults.Am J Respir Crit Care Med1998;158,1384-1387. [PubMed]
 
Troosters, T, Gosselink, R, Decramer, M Six minute walking distance in healthy elderly subjects.Eur Respir J1999;14,270-274. [PubMed]
 
DeBrock, V, Mets, T, Romagnoli, M, et al Captopril treatment of chronic heart failure in the very old.Gerontology1994;49,148-152
 
Lipkin, DP, Scrivin, AJ, Crake, T, et al Six minute walking test for assessing exercise capacity in chronic heart failure.BMJ1986;292,653-655. [PubMed]
 
Bittner, V Six-minute walk test in patients with cardiac dysfunction.Cardiologia1997;42,897-902. [PubMed]
 
Franciosa, JA, Levine, TB Lack of correlation between exercise capacity and indices of resting LV performance in heart failure.Am J Cardiol1981;47,33-39. [PubMed]
 
Montgomery, PS, Gardner, AW The clinical utility of a six-minute walk test in peripheral arterial occlusive disease patients.J Am Geriatr Soc1998;46,706-711. [PubMed]
 
Mak, VHF, Bugler, JR, Roberts, CM, et al Effect of arterial oxygen desaturation on six minute walk distance, perceived effort, and perceived breathlessness in patients with airflow limitation.Thorax1993;48,33-38. [PubMed]
 
Wijkstra, PJ, TenVergert, EM, vanderMark, ThW, et al Relation of lung function, maximal inspiratory pressure, dyspnoea, and quality of life with exercise capacity in patients with COPD.Thorax1994;49,468-472. [PubMed]
 
Rantanen, T, Guralnik, JM, Rantala, RS, et al Disability, physical activity, and muscle strength in older women: The Women’s Health and Aging Study.Arch Phys Med Rehab1999;80,130-135
 
Sipila, S, Multanen, J, Kallinen, M, et al Effects of strength and endurance training on isometric muscle strength and walking speed in elderly women.Acta Physiol Scand1996;156,457-464. [PubMed]
 
Rikli, RE, Jones, CJ Functional fitness normative scores for community-residing older adults, ages 60–94.J Aging Phys Activity1999;7,162-181
 
American Thoracic Society. Guidelines for the six minute walk test.Am J Respir Crit Care Med2002;166,111-117. [PubMed]
 
Redelmeier, DA, Bayoumi, AM, Goldstein, RS, et al Interpreting small differences in functional status: the six minute walk test in chronic lung disease patients.Am J Respir Crit Care Med1997;155,1278-1282. [PubMed]
 

Figures

Figure Jump LinkFigure 1. The association of BMI by deciles with 6MWD. Note the shorter distance walked by obese elderly persons (BMI > 30).Grahic Jump Location
Figure Jump LinkFigure 2. The relationship between the AAI of systolic BP and 6MWD. A breakpoint was found at AAI of 1.10 for women and AAI of 1.20 for men.Grahic Jump Location
Figure Jump LinkFigure 3. The relationship of diastolic BP with 6MWD in elderly women. A breakpoint was found at a diastolic BP of 69 mm Hg.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Participation, Exclusions, and Completion of the 6MWT
Table Graphic Jump Location
Table 2. Comparison of Study Participants Who Completed the 6MWT, Partial Completers, and Those Who Were Not Tested*
* 

Data are presented as mean (SD) or %.

 

This category includes participants who came into the clinic but refused the test, or were excluded from the test, or were unable to perform the test because of physical, cognitive, or equipment problems.

 

p values are unadjusted, and test for a trend across the categories (four rows).

Table Graphic Jump Location
Table 3. Symptoms Reported at the End of the 6MWT*
* 

Data are presented as No./total (%) or No. (%).

 

The majority of these symptoms involved muscle or joint pain, discomfort, or fatigue (n = 184). Other symptoms also included shortness of breath, tightness or pressure in chest, wheezing (n = 27); general weakness or fatigue (n = 26); dizziness or balance problems (n = 14); nausea (n = 6); and miscellaneous symptoms (n = 31). Some participants reported more than one symptom at the end of the test.

Table Graphic Jump Location
Table 4. Bivariate Associations With the Distance Walked During the 6MWT*
* 

Data are presented as mean (SD) or %. ln = natural log.

 

Unadjusted p values, testing for a trend across the quintiles of total distance walked.

 

Data are missing for these echocardiography variables from many subjects.

Table Graphic Jump Location
Table 5. Linear Regression Models Predicting 6MWD for Women (n = 1,094), With Same Variables in Model for Men and Women*
* 

See Table 4 for expansion of abbreviation.

Table Graphic Jump Location
Table 6. Linear Regression Models Predicting 6MWD for Men (n = 715), With Same Variables in Model for Men and Women*
* 

See Table 4 for expansion of abbreviation.

Table Graphic Jump Location
Table 7. Reference Equations for the 6MWD From the Healthy Subset of 437 Women and 315 Men
* 

Gender-specific cutpoints for obesity were > 90 kg for women and 101 kg for men, and for high waist size 118.5 cm for women and 116 cm for men.

References

Guralnik, J, Branch, L, Cummings, S, et al (1989) Physical performance measures in aging research.J Gerontol Med Sci44,M141-M146
 
Peeters, P, Mets, T The 6 minute walk as an appropriate exercise test in elderly patients with chronic heart failure.J Gerontol1996;51A,M147-M151
 
Jette, AM, Jette, DU, Ng, J, et al Are performance-based measures sufficiently reliable for use in multicenter trials?J Gerontol1999;54A,M3-M6
 
McGavin, CR, Artvinli, M, Naoe, H, et al Dyspnea, disability, and distance walked: comparison of estimates of exercise performance in respiratory disease.BMJ1978;2,241-243. [PubMed] [CrossRef]
 
Bittner, V, Weiner, DH, Yusuf, S, et al Prediction of mortality and morbidity with a six minute walk test in patients with left ventricular dysfunction.JAMA1993;270,1702-1707. [PubMed]
 
Hirsch, CH, Fried, LP, Harris, T, et al Correlates of performance-based measures of muscle function in the elderly: The Cardiovascular Health Study.J Gerontol1997;52A,M192-M200
 
Fried, LP, Borhani, NO, Enright, PL, et al The Cardiovascular Health Study: design and rationale.Ann Epidemiol1991;1,263-276. [PubMed]
 
Tell, GS, Fried, LP, Hermanson, B, et al Recruitment of adults 65 years and older as participants in the Cardiovascular Health Study.Ann Epidemiol1993;3,358-366. [PubMed]
 
Psaty, BM, Lee, M, Savage, PJ, et al Assessing the use of medications in the elderly: methods and initial experience in the Cardiovascular Health Study.J Clin Epidemiol1992;45,683-692. [PubMed]
 
Orme, J, Reis, J, Herz, E Factorial and discriminate validity of the CES-D scale.J Clin Psychol1986;42,28-33. [PubMed]
 
Cohen, S, Mermelstein, R, Kamarck, T, et al Measuring the functional components of social support. Saranson, IG Saranson, BR eds. Social support: theory, research and application. 1985; Martinus Nijhoff. Dordrecht, The Netherlands:.
 
Teng, EL, Chui, HC The modified Mini-Mental State (3MS) Examination.J Clin Psychol1987;48,314-318
 
Newman, AB, Siscovick, DS, Manolio, TA, et al Ankle-arm index as a marker of atherosclerosis in the Cardiovascular Health Study.Circulation1993;88,837-845. [PubMed]
 
Tracy, RP, Bovill, EG, Fried, LP, et al The distribution of coagulation factors VII and VIII and fibrinogen in adults over 65 years old: results for the Cardiovascular Health Study.Ann Epidemiol1992;2,509-519. [PubMed]
 
Tracy, RP, Lemaitre, R, Psaty, BM, et al Relationship of C-reactive protein to risk of cardiovascular disease in the Cardiovascular Health Study.Arterioscler Thromb Vasc Biol1997;17,1121-1127. [PubMed]
 
Gardin, JM, Wong, ND, Bommer, W, et al Echocardiographic design of a multicenter investigation of free-living elderly subjects: The Cardiovascular Health Study.J Am Soc Echocardiogr1992;5,63-72. [PubMed]
 
Furberg, CD, Manolio, TA, Psaty, BM, et al Major electrocardiographic abnormalities in persons aged 65 years and older: The Cardiovascular Health Study.Am J Cardiol1992;69,1329-1335. [PubMed]
 
O’Leary, DH, Polak, JF, Wolfson, SK, et al Use of sonography to evaluate carotid atherosclerosis in the elderly: Cardiovascular Health Study.Stroke1991;22,1155-1163. [PubMed]
 
Ives, DG, Fitzpatrick, AL, Bild, DE, et al Surveillance and ascertainment of cardiovascular events: The Cardiovascular Health Study.Ann Epidemiol1995;5,278-285. [PubMed]
 
American Thoracic Society. Standardization of spirometry, 1987 update.Am Rev Respir Dis1987;136,1285-1298. [PubMed]
 
Enright, PL, Kronmal, RA, Higgins, M, et al Spirometry reference values for women and men 65–85 years of age: Cardiovascular Health Study.Am Rev Respir Dis1993;147,125-133. [PubMed]
 
American Thoracic Society. Recommended respiratory disease questionnaires for use with adults and children in epidemiological research.Am Rev Respir Dis1978;6(part 2),7-23
 
Butland, RJA, Pang, J, Gross, ER, et al Two, six, and 12 minute walking tests in respiratory disease.BMJ1982;284,1607-1608. [PubMed]
 
Wilson, RC, Jones, PW A comparison of the visual analogue scale and modified Borg scale for the measurement of dyspnea during exercise.Clin Sci1989;76,277-282. [PubMed]
 
Tibshirani, R Estimating transformations for regression via additivity and variance stabilization.J Am Stat Assoc1988;83,394-405
 
Norusis, MJ. SPSS for Windows, base system user’s guide, release 9.0. 1998; SPSS. Chicago, IL:.
 
 S-Plus guide to statistical and mathematical analysis, version 3.2. 1993; StatSci. Seattle, WA:.
 
Cooper, KH A means of assessing maximal oxygen intake.JAMA1968;203,201-204. [PubMed]
 
McGavin, CR, Gupta, SP, McHardy, GJR Twelve minute walking test for assessing disability in chronic bronchitis.BMJ1976;1,822-823. [PubMed]
 
Langenfeld, H, Schneider, B, Grimm, W, et al The six minute walk test: an adequate exercise test for pacemaker patients?Pacing Clin Electrophysiol1990;13,1761-1765. [PubMed]
 
Spence, DPS, Hay, JG, Carter, J, et al Oxygen desaturation and breathlessness during corridor walking in COPD: effect of oxitropium bromide.Thorax1993;48,1145-1150. [PubMed]
 
Bernstein, ML, Despars, JA, Singh, NP, et al Re-analysis of the 12 minute walk in patients with COPD.Chest1994;105,163-167. [PubMed]
 
Montgomery, PS, Gardner, AW The clinical utility of a six minute walk test in peripheral arterial occlusive disease patients.J Am Geriatr Soc1998;46,706-711. [PubMed]
 
Fleg, JL, Lakatta, EG Role of muscle loss in the age-associated reduction in Vo2max.J Appl Physiol1988;65,1147-1151. [PubMed]
 
Tolep, K, Kelsen, SG Effect of aging on respiratory skeletal muscles.Clin Chest Med1993;3,363-378
 
Teramoto, S, Ohga, E, Ishii, T, et al Reference value of six-minute walking distance in healthy middle-aged and older subjects [letter].Eur Respir J2000;15,1132-1133. [PubMed]
 
Enright, PL, Sherrill, DL Reference equations for the six minute walk in healthy adults.Am J Respir Crit Care Med1998;158,1384-1387. [PubMed]
 
Troosters, T, Gosselink, R, Decramer, M Six minute walking distance in healthy elderly subjects.Eur Respir J1999;14,270-274. [PubMed]
 
DeBrock, V, Mets, T, Romagnoli, M, et al Captopril treatment of chronic heart failure in the very old.Gerontology1994;49,148-152
 
Lipkin, DP, Scrivin, AJ, Crake, T, et al Six minute walking test for assessing exercise capacity in chronic heart failure.BMJ1986;292,653-655. [PubMed]
 
Bittner, V Six-minute walk test in patients with cardiac dysfunction.Cardiologia1997;42,897-902. [PubMed]
 
Franciosa, JA, Levine, TB Lack of correlation between exercise capacity and indices of resting LV performance in heart failure.Am J Cardiol1981;47,33-39. [PubMed]
 
Montgomery, PS, Gardner, AW The clinical utility of a six-minute walk test in peripheral arterial occlusive disease patients.J Am Geriatr Soc1998;46,706-711. [PubMed]
 
Mak, VHF, Bugler, JR, Roberts, CM, et al Effect of arterial oxygen desaturation on six minute walk distance, perceived effort, and perceived breathlessness in patients with airflow limitation.Thorax1993;48,33-38. [PubMed]
 
Wijkstra, PJ, TenVergert, EM, vanderMark, ThW, et al Relation of lung function, maximal inspiratory pressure, dyspnoea, and quality of life with exercise capacity in patients with COPD.Thorax1994;49,468-472. [PubMed]
 
Rantanen, T, Guralnik, JM, Rantala, RS, et al Disability, physical activity, and muscle strength in older women: The Women’s Health and Aging Study.Arch Phys Med Rehab1999;80,130-135
 
Sipila, S, Multanen, J, Kallinen, M, et al Effects of strength and endurance training on isometric muscle strength and walking speed in elderly women.Acta Physiol Scand1996;156,457-464. [PubMed]
 
Rikli, RE, Jones, CJ Functional fitness normative scores for community-residing older adults, ages 60–94.J Aging Phys Activity1999;7,162-181
 
American Thoracic Society. Guidelines for the six minute walk test.Am J Respir Crit Care Med2002;166,111-117. [PubMed]
 
Redelmeier, DA, Bayoumi, AM, Goldstein, RS, et al Interpreting small differences in functional status: the six minute walk test in chronic lung disease patients.Am J Respir Crit Care Med1997;155,1278-1282. [PubMed]
 
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