IntroductionIn obese subjects, the relative reduction of the skeletal muscle strength, the reduced cardio-pulmonary capacity and tolerance to effort, the higher metabolic costs and, therefore, the increased inefficiency of gait together with the increased prevalence of co-morbid conditions might interfere with walking. Performance tests, such as the six-minute walking test (6MWT), can unveil the limitations in cardio-respiratory and motor functions underlying the obesity-related disability. Therefore the aims of the present study were: to explore the determinants of the 6-minute walking distance (6MWD) and to investigate the predictors of interruption of the walk test in obese subjects.MethodsObese patients [body mass index (BMI)>40 kg/m2] were recruited from January 2009 to December 2011. Anthropometry, body composition, specific questionnaire for Obesity-related Disabilities (TSD-OC test), fitness status and 6MWT data were evaluated. The correlation between the 6MWD and the potential independent variables (anthropometric parameters, body composition, muscle strength, flexibility and disability) were analysed. The variables which were singularly correlated with the response variable were included in a multivariated regression model. Finally, the correlation between nutritional and functional parameters and test interruption was investigated.Results354 subjects (87 males, mean age 48.5±14 years, 267 females, mean age 49.8±15 years) were enrolled in the study. Age, weight, height, BMI, fat mass and fat free mass indexes, handgrip strength and disability were significantly correlated with the 6MWD and considered in the multivariate analysis. The determination coefficient of the regression analysis ranged from 0.21 to 0.47 for the different models. Body weight, BMI, waist circumference, TSD-OC test score and flexibility were found to be predictors of the 6MWT interruption.DiscussionThe present study demonstrated the impact of disability in obese subjects, together with age, anthropometric data, body composition and strength, on the 6-minute walking distance.

The correlation between the 6-minute walking distance and obesity has been only partially explored. Results obtained from the existing predictive equations are influenced by a variety of factors (health status, severity of obesity, reduced muscle strength and mobility, decreased aerobic capacity, presence of comorbidities).The aim of our study was to verify, compare and discuss the 6MWD predictive capacity of the equations currently available in the literature in a sample of obese subjects.Despite similar study design, the considered articles varied with regard to the number of individuals included and to age range. None of the equations available in the literature was able to accurately predict the six-minute walked distance performed by the obese subjects involved in our study. The six-minute walked distance performed by obese subjects seems to be influenced by other factors than the variables included in the equations from the literature, suggesting that they may not thoroughly capture the complexity of disability in obese people. Future research should be designed in order to validate population-specific equations, by including variables related to clinical, functional, and psychological areas, which are usually impaired in obese individuals.