Reproducibility of the 6-minute Walk Test in Obese Adults

Abstract

The six-minute walk test (6MWT) is an inexpensive, quick and safe tool to evaluate the functional capacity of patients with heart failure and chronic obstructive pulmonary disease. The aim of this study was to determine the reproducibility of the 6MWT in overweight and obese individuals. We thus undertook a prospective repeated-measure validity study taking place in our academic weight management outpatient clinic. The 6MWT was conducted twice the same day in 21 overweight or obese adult subjects (15 females and 6 males). Repeatability of walking distance was the primary outcome. Anthropometric measures, blood pressure and heart rate were also recorded. Participant's mean BMI was 37.2+/-9.8 kg/m(2) (range: 27.0-62.3 kg/m(2)). Walking distance in the morning (mean=452+/-90 m) and in the afternoon (mean=458+/-97 m) were highly correlated (r=0.948; 95% Confidence Interval 0.877-0.978; p<0.001). Walking distance was negatively correlated with BMI (r=-0.47, p=0.03), waist circumference (r=-0.43, p=0.05) and pre-test heart rate (r=-0.54, p=0.01). Our findings indicate that the 6MWT is highly reproducible in obese subjects and could thus be used as a fitness indicator in clinical studies and clinical care in this population.

Critical review of the equations predicting 6-minute walking distance in obese subjects

“…Beriault et al [28] reported that, although BMI is negatively correlated with the distance walked during 6MWT, the actual distance measured in their sample was shorter than in other studies, suggesting that cardiopulmonary fitness of their participants was poorer than in other studies.…”

“…Few studies have explored the performance during the 6MWT in obese subjects [28][29][30][31]. Despite high reproducibility, results from these studies are influenced by a wealth of factors, including health status, severity of obesity, reduced muscle strength and mobility, decreased aerobic capacity and presence of comorbidities, with special regard to pulmonary and cardiovascular diseases.…”

“…Even if age was taken into account as explanatory variable by those Authors [29], the equation was validated in a sample whose age was below 60 years, thus reducing the predictive validity for elderly subjects. Two studies suggest that 6MWT seems to be highly reproducible and reliable in overweight and obese individuals [28,31] and that it could be used to quantify some aspects of the functional capacity of obese patients and to monitor changes in fitness over the course of weight management interventions. Obesity increases the work load for a given amount of exercise, probably resulting in the shorter distances walked by women with a higher body weight or BMI; moreover, both body weight and BMI were significant when entered into the models [18,20].…”

“…Obesity increases the work load for a given amount of exercise, probably resulting in the shorter distances walked by women with a higher body weight or BMI; moreover, both body weight and BMI were significant when entered into the models [18,20]. Other studies reported [25,28,30,37] significant correlations between the distance walked during 6MWT and height, body weight, and BMI. On the contrary, Poh et al [39] failed to show an inverse relationship between BMI and the distance at the 6MWT.…”

Correlation of Self-Reported Breathlessness with Post Exercise Dyspnea in Obesity

“…Other tools such as the Borg dyspnea scale is used for quantitative assessment [10]. The 6 MWT has shown good reproducibility and could be used as a fitness indicator in clinical studies in the obese population [11] [12]. Establishing a correlation between qualitative pre-exercise score (mMRC scale) and quantitative post exercise score (Borg scale) would validate the use of dyspnea questionnaire in the assessment of obese breathlessness.…”