Disability Affects the 6-Minute Walking Distance in Obese Subjects (BMI.40 kg/m 2 ) Lorenzo Maria Donini 1 *, Eleonora Poggiogalle 1 , Veronica Mosca 1 , Alessandro Pinto 1 , Amelia Brunani 2 , Paolo Capodaglio 2 1 Department of Experimental Medicine–Medical Physiopathology, Food Science and Endocrinology Section, ‘‘Sapienza’’ University of Rome, Rome, Italy, 2 Rehabilitation Unit and Research Laboratory in Biomechanics and Rehabilitation, Istituto Auxologico Italiano IRCCS, Piancavallo, Verbania, Italy Abstract Introduction: In 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. Methods: Obese patients [body mass index (BMI).40 kg/m 2 ] 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. Results: 354 subjects (87 males, mean age 48.5614 years, 267 females, mean age 49.8615 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. Discussion: The 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. Citation: Donini LM, Poggiogalle E, Mosca V, Pinto A, Brunani A, et al. (2013) Disability Affects the 6-Minute Walking Distance in Obese Subjects (BMI. 40 kg/m 2 ). PLoS ONE 8(10): e75491. doi:10.1371/journal.pone.0075491 Editor: Reury F.P. Bacurau, University of Sao Paulo, Brazil Received April 17, 2013; Accepted August 14, 2013; Published October 11, 2013 Copyright: ß 2013 Donini et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: No current external funding sources for this study. Competing Interests: The authors have declared that no competing interests exist. * E-mail: lorenzomaria.donini@uniroma1.it Introduction In obese subjects, the relative reduction of the skeletal muscle strength [1], the reduced cardio-pulmonary capacity and tolerance to effort [2,3], the higher metabolic costs and, therefore, the increased inefficiency of gait [4], together with the increased prevalence of co-morbid conditions, might interfere with walking. Pain from overloaded joints [5–7] is a frequent complaint during walking in obese subjects, who tend to walk slower and report more frequently dyspnea than their lean counterparts [8]. On the other hand, walking often represents the most accessible mean of exercise for weight management. The ability to walk for a distance is a quick and inexpensive measure of physical function, and an important component of quality of life, since it reflects the capacity to undertake the activities of daily living [4,5]. 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 [2,3]. After the publication of the 6MWT official guidelines elaborated by the American Thoracic Society in 2002, several authors studied the determinants of the 6-minute walking distance (6MWD) in healthy adults. Predictive equations considering age, sex, weight and height were proposed for clinical use [9–13]. They aimed at representing a reference test for populations with different ethnicities and clinical conditions. These studies varied with respect to the number of individuals (with the exception of two large ones) [14,15] but presented similar design and the reference equations were obtained using linear multiple regression models, including demographic and anthropometric features (age, sex, stature and weight in almost all studies) [16]. Only few studies correlated the 6MWD and severity of obesity; moreover, despite results were shown to be highly reproducible, they also demonstrated that they PLOS ONE | www.plosone.org 1 October 2013 | Volume 8 | Issue 10 | e75491