Disability Affects the 6-Minute Walking Distance in Obese Subjects (BMI>40 kg/m(2)).
ABSTRACT 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.
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.
354 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.
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.
- SourceAvailable from: Antonio AversaEating and weight disorders: EWD 03/2014; · 0.53 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Obesity is a chronic disease as well as a risk factor for cardiovascular, metabolic and osteoarticular diseases, affecting the psychosocial health and the quality of life. Recent evidence suggests that the adequate treatment of obesity should provide a multidimensional multidisciplinary approach including nutritional therapy, psycho-educational classes and physical reconditioning/motor rehabilitation. The aim of this approach should be to maintain the results over time with a positive impact on the obesity-related cardiovascular and metabolic risk. To evaluate the effectiveness of a multidisciplinary Nutritional and Psycho-Physical Reconditioning Program (NPPRP) in an outpatient setting. The observational prospective cohort study involved subjects, aged from 18 to 65 years, with a BMI >30 kg/m(2), who were followed up over 48 months. After the first nutritional and psychological examination, patients who refused NPPRP were treated according to standard nutrition procedures (SNT). Patients were followed through monthly medical examinations and then by annual telephonic structured interviews for 4 years. Changes in body weight, eating behavior, physical activity performance, and the occurrence of clinical obesity-related complications were considered as outcome measures. Of 464 enrolled patients, 161 (34.7 %) took part in the follow-up. From the enrollment to the end of follow-up, weight loss was greater in the NPPRP group than in the SNP group (-8.08 ± 10 kg versus -3.0 ± 6 kg). After 4 years eating behavior improved in both groups. The percentage of patients who continued to perform physical activity was higher in the NPPRP group than in the SNT group (61.0 versus 34.1 %). The SNT group reported complications more frequently than the NPPRP group: hypertension (19 versus 5.8 %), dyslipidemia (19.4 versus 12.7 %), and skeletal problems (26.9 versus 17.5 %). The main reasons for drop-out from the rehabilitation program were logistic problems (distance or time) in both groups; disappointment was higher in the SNT group than in the NPPRP group (37.8 versus 15.6 %). A multidimensional multidisciplinary approach including nutritional intervention and psycho-physical rehabilitation, set against a conventional diet therapy, was more effective in the long-term outcome of obesity with regard to weight loss, physical activity, possible eating disorders, and obesity-related complications.Eating and weight disorders: EWD 03/2014; · 0.53 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: In recent years, mounting interest has been directed to sarcopenic obesity (SO), given the parallel increase of life expectancy and prevalence of obesity in Western countries. The phenotype of SO is characterized by the coexistence of excess fat mass and decreased muscle mass, leading to the impairment of physical performance. The aim of the present review was to summarize the impact of different treatment strategies contrasting body composition changes in older obese and overweight subjects, providing insight into the SO phenotype. Revision questions were formulated; relevant articles were identified from Pubmed through a systematic search strategy: definition of the search terms (sarcopenic obesity, diet, nutritional supplements, physical activity, exercise, pharmacological treatment); limits: papers published in the last 10 years; humans; age ≥ 60 years old; body mass index >25 kg/m(2); language: English. Studies dealing with sarcopenia associated to cancer cachexia or neurological diseases, any malignant disease, inflammatory or autoimmune diseases, corticosteroids for systemic use, bedridden subjects, and syndromic obesity were excluded. 14 articles were identified for inclusion in the present systematic review, and were grouped basing on the type of the main intervention: data assessing body composition changes after combined lifestyle interventions, exercise/physical activity, dietary interventions, and pharmacological treatment. Most of the studies were randomized, controlled. Sample size ranged from 12 to 439 subjects, and study duration varied from 6 weeks to 12 months. Weight loss based on diet combined with exercise seems to be the best strategy to adopt for treatment of phenotypic aspects of SO, improving metabolic consequences related to excess fat, preserving lean mass, and allowing functional recovery.Endocrine. 06/2014;
Disability Affects the 6-Minute Walking Distance in
Obese Subjects (BMI. .40 kg/m2)
Lorenzo Maria Donini1*, Eleonora Poggiogalle1, Veronica Mosca1, Alessandro Pinto1, Amelia Brunani2,
1Department of Experimental Medicine–Medical Physiopathology, Food Science and Endocrinology Section, ‘‘Sapienza’’ University of Rome, Rome, Italy, 2Rehabilitation
Unit and Research Laboratory in Biomechanics and Rehabilitation, Istituto Auxologico Italiano IRCCS, Piancavallo, Verbania, Italy
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/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.
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/m2). 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: ? 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: firstname.lastname@example.org
In obese subjects, the relative reduction of the skeletal muscle
strength , the reduced cardio-pulmonary capacity and tolerance
to effort [2,3], the higher metabolic costs and, therefore, the
increased inefficiency of gait , 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 . 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
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) . 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.org1 October 2013 | Volume 8 | Issue 10 | e75491
were influenced by the severity of obesity, reduced strength and
aerobic capacity [17,18].
According to the predictive equations from the literature, obese
subjects consistently show a deficit in the distance walked and in
work exerted for walking when compared with normal-weight
subjects . Reference values obtained from healthy, normal-
weight populations would therefore predictably underline the
reduced performance capacity of obese individuals. Instead,
reference values specific for this population would serve as a
benchmark to assess baseline functional capacity, to prescribe
proper and safe exercise intensity and to supervise changes after
rehabilitation interventions. Recently Capodaglio et al. 
developed a reference equation for predicting the 6MWD
specifically in adult obese subjects to be used in the clinical
practice. Clinical applicability of the test represented, for many
authors, the guiding criterium for avoiding inclusion of other
parameters correlated with the results of the walking test. From a
mathematical point of view, the correlation with the 6MWD
would certainly benefit from the inclusion of several other factors
in the predictive formula. Hulens et al.  found that 75% of the
variance in walking performance was explained by the combina-
tion of the following variables: body mass index (BMI), peak
aerobic capacity, knee extension torque, age, hours of TV viewing,
BMI explaining 59% of the variance by itself. Among the
predictors of the distance walked, other physiological (heart rate,
oxygen saturation, blood pressure, muscle strength), life style
(physical activity levels) factors and degree of disability may well
play a role. Although their inclusion in an equation appears
unpractical for clinical use, we need to further investigate the
determinants of distance walked by obese individuals, as it would
result likely in an increased prediction capacity of the equation and
a deeper comprehension of the limitations of obese subjects. Also,
pre- and post-assessments after combined interventions in obese
subjects revolve around the main expected outcome of weight loss.
The expected functional correlation is an increase in the distance
walked secondary to weight loss. However, if co-morbid disabling
conditions are present, distance might not necessarily increase, as
expected on the basis of weight loss solely. Otherwise, if weight loss
is accompanied by an improved tolerance to the effort after
aerobic conditioning, the formula may underestimate the real
performance. Hence, we hypothesized that the degree of disability
of obese subjects should be part of their functional assessment. In
fact, their disability was shown to affect the basic activities of daily
living and to be mainly related to mobility impairment. Recently,
an obesity-specific disability scale was developed  and it was
also demonstrated to be able in measuring changes after
multidisciplinary rehabilitation interventions [21,22]. Therefore,
the aims of the present study were: to further explore the
determinants of the 6MWD by obese subjects and in particular
whether measures of disability would affect the results; and to
investigate the predictors of interruption of the walk test in obese
Caucasian adult obese patients (BMI.40 kg/m2) were recruit-
ed at the Metabolic, Nutritional and Psychological Rehabilitation
Unit at ‘‘Villa delle Querce’’ Clinical and Rehabilitation Institute
(Nemi, Rome-Italy) from January 2009 to December 2011, among
all the obese patients hospitalised in the facility during the above
mentioned period. Eligibility criteria for patients to be admitted to
an intensive rehabilitation treatment were: BMI.40 kg/m2
associated to a significant disability level [as assessed by the
TSD-OC test (SIO Test assessing disabilities obesity related), see
above, with a disability score.33% -  and the presence of at
least one clinical comorbidity. Patients aged less than 18 years and
more than 80 years were excluded from the study. In addition,
bed-ridden patients and patients presenting contraindications for
the 6MWT (acute cardiac diseases in the previous month, unstable
angina, uncontrolled hypertension (higher than 180/100 mmHg),
major othopaedic or neurological conditions interfering with the
test) were excluded .
The study protocol was approved by the Ethical Committee of
the ‘‘Sapienza’’ University of Rome and oral and written informed
consent was obtained from all the subjects.
The following data were measured within the first week after the
N anthropometric measures, according to the procedures de-
scribed in the ‘‘Anthropometric standardisation reference
manual’’ by Lohman et al. , by a trained operator. Body
weight was measured to the nearest 0.1 kg using a standard
column body scale SECA (Hamburg, Germany). Body height
(using a rigid stadiometer – SECA, Hamburg, Germany), waist
and arm circumferences (WC and AC respectively) (using a
measuring tape) were determined to the nearest 0.1 cm.
Triceps skinfold thickness (TSF) was measured using a
Harpenden Skinfold Caliper (British Indicators Ltd, St.
Albans, Herts, UK).
Then, the following indexes were calculated:
N BMI= weight/height in kg/m2
N mid-upper arm muscle circumference =AC - (p * TSF)
N Body composition [fat mass (FM) and fat free mass (FFM)] was
estimated by bioelectrical impedance analysis (BIA): whole-
body impedance vector components, resistance (R) and
reactance (Xc), were measured with a single-frequency 50-
kHz analyzer STA-BIA (AKERN Bioresearch SRL, Pontas-
sieve, FL, Italy). Measurements were obtained following
standardized procedures . The external calibration of the
instrument was checked with a calibration circuit of known
impedance value. Estimations of FFM and FM by BIA were
obtained using sex-specific, BIA prediction equations devel-
oped by Sun et al. in a large population including extremes of
BMI values . Fat mass index (FMI) and fat-free mass index
(FFMI) were calculated as FM or FFM in kg/body height in
N Specific short-form questionnaire for Obesity-related Disabil-
ities (TSD-OC test) proposed by the Italian Society of Obesity
was fulfilled by all the participants . The TSD-OC test
addresses adults and does not target a specific sex. It is
composed by 7 sections (pain: 5 items; stiffness: 2 items;
activities of daily living and indoor mobility: 7 items;
housework: 7 items; outdoor activities: 5 items; occupational
activities: 4 items; social life: 6 items) for a total of 36 items.
Patients were requested to subjectively assess their difficulty in
each item by means of a 0–10 visual analogue scale (10
indicating the highest level of disability and 0 no difficulties in
performing the task). The total score (0 to 360) represents the
disability status of the patient;
N Fitness status was assessed by:
6-Minute Walking Distance in Obese Subjects
PLOS ONE | www.plosone.org2 October 2013 | Volume 8 | Issue 10 | e75491
N hand grip strength (HGST), measured using a Lafayette
hand grip (Mod. 78011). The maximum value (kg) out of
three trials using the dominant hand was recorded. Between
two consecutive trials, a 1-minute recovery was provided
N Spine flexion, together with hip and shoulder flexion,
extension, and abduction were measured with a standard
goniometer by a skilled physiotherapist. The floor-fingertip
distance (in centimeters) was considered as a measure of
N The 6MWT was performed according to the instructions by
the American Thoracic Society . In particular, conditions
for the execution of a safe test were respected: an easily
accessible corridor for emergencies, the test interruption
criteria, such as chest pain, severe dyspnea, muscle cramps,
dizziness, and sudden paleness, were considered when
applicable. The test was performed in an undisturbed 20-
meter hospital corridor marked every 2 meters with colored
tape on the floor; starting and finishing points were marked on
the floor. Before the test, at 1, 3 and 5 minutes after the start
and at the end of the test, pulse, respiratory rate, blood
pressure and perceived fatigue on Borg’s scale were measured
. Subjects were instructed to walk as fast as they could.
They were allowed to stop or rest during the test if necessary.
The 6MWD was calculated.
First, the correlations between 6MWD and the potential
independent variables (anthropometric parameters, body compo-
sition, muscle strength, flexibility and disability) were analysed.
After verification of the normal distribution of the variables, t-test
and the analysis of variance (ANOVA) were performed to describe
differences between means of the groups, and chi-square test was
used to compare observed and expected frequencies. A linear
regression analysis (Pearson’s r) was performed to verify the
association among continuous variables.
In a second phase, the variables which were singularly
correlated with the response variable were included in a group
of potential explicative elements of a multivariated regression
model using the variables with the highest correlations and
excluding the redundant ones to minimize the confounding effect
of collinearity, in accordance with the principle of parsimony.
The multiple linear regression models obtained were expressed
in the following algebraic form
where ‘‘y’’ represents the outcome variable (6MWD), ‘‘x’’ the
values of the independent variables, ‘‘b’’ the unstandardized
coefficients of the independent variable and a the constant
The efficacy of the regression model was analysed according to
the value of the determination coefficient R2(comparing the
explained variance of the model’s predictions with the total
variance of the data) and the R2adjusted (considering a correction
for inclusion of variables). The standard error of the estimate
(SEE), representing a measure of the accuracy of predictions
(standard deviation of the differences between the actual values of
the dependent variables (results) and the predicted values), was
Finally, the correlations between nutritional and functional
parameters and test interruption were investigated.
Differences were considered to be statistically significant at
p,0.05. Statistical analysis was performed using SPSS 10.0
statistical software (SPSS Inc Wacker Drive, Chicago, IL, USA).
Characteristics of the study sample (Table 1)
354 subjects (87 males, mean age 48.5614 years - range 19–74
years, 267 females, mean age 49.8615 years - range 19–80 years)
were enrolled in the study. All of the subjects had a BMI.40 kg/
m2(44.768 versus 43.768 kg/m2, respectively for males and
females) with a significantly increased WC (133.3613 versus
117.8615 cm, respectively for males and females; p,0.05).
Statistically significant differences (p,0.05) were found between
males and females, in particular for the 6MWD (444.36106 versus
418.8680 m), handgrip strength (36.767 versus 25.466 kg) and
Deteminants of the 6MWD
In Table 2, the correlations between the considered variables
and the distance walked are described. Based on these results, a
multivariate regression analysis was performed using only the
independent variables significantly correlated with the outcome
variables at the univariate analysis: age, weight, height, BMI, FMI,
FFMI, HGST and disability (TSD-OC test score). Variables
showing a lower correlation with analogous biological meaning
were excluded. Sex was not part of the predictive model: distance
walked by males and females did not significantly differ in our
sample (Table 1). Data from the elaborated models and indicators
of the precision in describing the 6MWT results are reported in
Table 3. The R2of the regression analysis ranged from 0.21 of the
model 1 considering only HGST and TSD-OC (SEE: 82.0 m) to
0.47 for the model 5 considering also age, FMI and FFMI (SEE:
66.7 m). Slightly lower results were obtained with models using
BMI or body weight and height. Model 5 showed a significant
correlation with the real distance walked by patients (r=0.644;
p,0.001): the mean difference between real and predicted results
was 38.7679 m (range 242.5 m to 106.1 m).
Predictors of the 6MWT interruption (Table 4)
15 males (17.2%) and 54 females (30.2%) interrupted the test
according to the described criteria (p.0.05).
Obese men who interrupted the test showed a higher body
weight (144.2633 versus 131.1618 kg), BMI (49.567 versus
44.167 kg/m2)andWC (143.5616
(p,0.05) than the rest of the sample. Disability as measured by
TSD-OC test was more severe: 48.7622 versus 27.4626%
(p,0.05). Flexibility, except for spine flexion, were significantly
lower (p,0.05). Although non-significantly, among those who
interrupted the test, HGST showed a tendency to be lower and
Obese women who interrupted the test showed a higher body
weight (121.3623 versus 106.8620 kg), BMI (47.769 versus
43.467 kg/m2), a larger WC (126.4617 versus 117.2614 cm)
and higher FM (47.664 versus 44.864%) than obese women
completing the test (p,0.05). The degree of disability was also
higher (44.1628 versus 33.5624%; p,0.05), whereas HGST
(25.467 vs 27.265 kg) and flexibility were significantly lower
(p,0.05). Males and females did not differ significantly with
respect to age.
6-Minute Walking Distance in Obese Subjects
PLOS ONE | www.plosone.org3 October 2013 | Volume 8 | Issue 10 | e75491
The present study demonstrated the impact of the degree of
disability in obese subjects on the 6MWD. The latter was
correlated to the following variables: age, anthropometric data
(body weight, height, BMI), body composition (FMI, FFMI),
strength (HGST) and disability (TSD-OC test).
Previously several authors addressed the identification of
determinants of the 6MWD by healthy adults and proposed
reference equations. The large majority of them considered only
body height, age and body weight . Troosters et al. 
concluded that these variables accounted for 66% of the variance
in a sample of 53 healthy Caucasian adults aged 50 to 85 years,
who were not previously hospitalized and did not show any
chronic condition potentially hindering physical capacity .
Enright  performed the 6MWT in 290 healthy adults aged 40
to 80 years with BMI,35 kg/m2, finding a significant difference
depending on height, sex and age. There is a general consensus
about the fact that shorter individuals and females present a
shorter step length and, consequently, shorter distances walked at
the 6MWT. Likewise, in elderly sarcopenic individuals, similarly
to patients with cognitive impairment or musculoskeletal disorders,
reduction in the 6MWD was described [14,30].
Muscle strength, depression, reduced perceived quality of life,
medications, inflammatory disease and impaired pulmonary
function are other factors that can influence the test performance
[31–34]. In particular, in a study done by Enright and Sherrill ,
a BMI.30 kg/m2was considered an exclusion criterium, since
the research addressed the adult healthy population. Also a paper
by Hulens et al.  was in line with these considerations,
underlining that the test results were highly affected by the degree
of obesity. Ben Saad et al.  showed that when BMI was
included in the final reference equation, the 6MWD decreased by
5.27 meters when BMI increased by one unit. In a later study ,
Table 1. Demographic and functional characteristics of the entire sample (n=354).
N 87 267
Anthropometry and body composition Weight (kg)134.1622 111.1621*
BMI (kg/m2)44.768 43.768
AC (cm) 39.36441.465
WC (cm)133.3613 117.8615*
FMI (kg/m2)18.963 23.263*
FFMI (kg/m2)26.064 20.863*
Function6MWD (m) 1
Hand grip strength (kg)37.967 26.866*
Articular mobilitySpine flexion (cm)17.761011.4611*
Hip flexion - right (6)
Hip flexion – left (6)
Hip extension - right (6)
Hip extension – left (6)
Hip abduction - right (6)
Hip abduction - left (6)
1The data refer only to persons who have completed the 6MWT (M:74, F:221)
*p,0.05: t test: males versus females
Legend: BMI: body mass index; TSF: triceps skinfold thickness; AC: arm circumference; MAMC: mid-upper arm muscle circumference; WC: waist circumference; FMI: fat
mass index: FFMI: fat-free mass index; 6MWD: six-minute walking distance; TSD-OC: specific short-form questionnaire for Obesity-related Disabilities proposed by the
Italian Society of Obesity.
6-Minute Walking Distance in Obese Subjects
PLOS ONE | www.plosone.org4October 2013 | Volume 8 | Issue 10 | e75491
Enright reported that the 6MWT results were affected by muscle
strength in individuals with reduced mobility and aerobic capacity.
Thus, our results are consistent with the extant literature: mobility
and muscle strength are key factors for predicting the 6MWD by
obese individuals. Body composition was considered relevant by
some authors in influencing results at the 6MWT, more
significantly than BMI per se [18,30]. Although the BMI is a
useful epidemiological index of obesity, it cannot be considered as
the best index to determine the amount of body fat. Moreover, the
correlation between body composition and the 6MWD is usually
Table 2. Correlation between 6-minutes walking distance and functional - nutritional parameters.
Antropometry and body composition Weight
Articular Mobility Spine flexion
Hip flexion - right
Hip flexion – left
Hip extension - right
Hip extension – left
Hip abduction - right
Hip abduction - left
The data refer only to persons who have completed the six-minute walk test (M:74, F:221)
Legend: BMI: body mass index; WC: waist circumference; AC: arm circumference; MAMC: mid-upper arm muscle circumference; TSF: triceps skinfold thickness; FMI: fat
mass index; FFMI: fat-free mass index; HGST: hand-grip strength test; TSD-OC: specific short-form questionnaire for Obesity-related Disabilities proposed by the Italian
Society of Obesity.
Table 3. Multivariate model correlating 6-minute walk distance (6MWD) to clinical and functional parameters.
Model 1Model 2 Model 3Model 4 Model 5
HGST3.110.20.000 2.140.540.0001.730.660.0082.730.49 0.0003.370.950.000
Intercept382.1718.60.000496.6126.90.00067.11108.00.524 670.59 31.90.000577.8248.1 0.000
R2adj0.21 0.28 0.370.41 0.45
Legend: HGST: hand grip strength test; TSD-OC: specific short-form questionnaire for Obesity-related Disabilities; BMI: body mass index; FMI: fat mass index; FFMI: fat-
free mass index; b: the unstandardized coefficients of the independent variable; R2: determination coefficient; SE: standard error; SEE: standard error of the estimate.
Example of regression equation: Model 1: 6MWD (m) =382.17+(3,11 * HGST) 2 (1.13 * TSD-OC).
6-Minute Walking Distance in Obese Subjects
PLOS ONE | www.plosone.org5October 2013 | Volume 8 | Issue 10 | e75491
more robust than the correlation between the 6MWD and BMI
[14,30,31,34]. In our sample, these data were confirmed, both
FMI and FFMI, and HGST correlating with the 6MWD. We also
aimed at ascertaining to what extent disability may affect test
results. In a previous study Enright  concluded that disability
in activities of daily living and occupational activities is an
important factor. Disability may impair the test performance also
at the emotional and psychological level, as it may induce
depression, which ultimately impacts on the 6MWT results,
according to several authors [14,35–37]. In fact, also the American
Thoracic Society in the guidelines published in 2002 ,
recommended the use of standardized encouragement to avoid
bias of the results, on the basis that improving the emotional state
may enhance 6MWD results by 30%. Despite significantly
correlated to the distance walked, the proposed multivariate
models explained less than half of the variance of the phenom-
enon. The other models in the literature show R2ranging from
0.20  to 0.78 . The population considered in our study
may in part explains the relatively low reliability of the model
proposed, despite the inclusion of variables all individually
correlated with the outcome variable. In fact our population
consisted of subjects admitted to a multidisciplinary metabolic-
nutritional rehabilitation due to the severe obesity-related comor-
bidities. They were in frail functional and clinical conditions.
Other variables more focused on the clinical aspects may perhaps
increase the validity of the model. Other authors [18,35–38]
commented that some features linked to specific comorbidities
may affect test results; our data about the subjects who were not
able to complete the 6MWT seem to be consistent. In fact, obese
subjects who failed in the test performance, showed a greater
functional impairment and disability, reduced muscle strength,
higher fat mass as compared to their counterparts who finished the
test. Therefore, the 6MWT appears more as a global performance
test than a mere measure of motor capacity. It remains true that
the implementation of those variables hinders the daily use of the
predictive equation in non-specialistic facilities. However, those
variables should be considered in the baseline assessment of obese
patients to optimize the rehabilitation programs and increase their
effectiveness. The variables adopted in our model define a more
complex equation than those already available in the literature,
however, the main goal of our study was not to provide an
evaluation tool for everyday practice, instead to highlight the
differences in the 6MWT results due to the disability correlated to
obesity and define the elements that may account for such different
performances, either causes or consequences of disability.
The present study has certain limitations that need to be taken
into account. Despite having acknowledged all the indications
suggested by the American Thoracic Society, the length of the
walkway we used in this study was shorter than that used by
Enright (20 versus 30 m) . This difference might have biased
the results, although it appears very unlikely, as already
commented by other authors , that this particular circum-
stance might have caused such a marked difference in the results.
In our study a greater number of females was enrolled. In the
literature, as in our study, males normally walk a longer 6MWD.
Although the distribution of FM, that is different between males
and females, may play a role in influencing this result, evidence
suggests that the impact of sex on joint mobility does not appear
relevant. Accordingly, in our sample, the correlation between
disability and 6MWD does not change as a function of sex.
Table 4. Nutritional and functional parameters in completers (C) and not completers (NC) the 6MWT.
C NCC NC
N 72 15213 54
Anthropometry and body
Weight (kg)131.1618 144.2633*106.8620121.3623*
BMI (kg/m2)44.16749.567* 43.46747.769*
AC (cm)38.16442.266*38.964 42.465*
MAMC (cm) 29.16331.26528.66431.365*
WC (cm) 132.6611 143.5616*117.2614126.4617*
FFMI (kg/m2) 25.163 26.86420.462 21.764
Articular mobilitySpine flexion (cm)18.76915.968 10.261014.6611*
Hip flexion - right (6)
Hip flexion – left (6)
Hip extension - right (6)
Hip extension – left (6)
Hip abduction - right (6)
Hip abduction - left (6)
DisabilityTSD-OC (%)27.4626 48.7622* 33.5624 44.1628*
Legend: 6MWT: six-minute walk test; BMI: body mass index; AC: arm circumference; MAMC: mid-upper arm muscle circumference; WC: waist circumference; FMI: fat mass
index: FFMI: fat-free mass index; HGST: hand grip strength test; TSD-OC: specific short-form questionnaire for Obesity-related Disabilities.
6-Minute Walking Distance in Obese Subjects
PLOS ONE | www.plosone.org6October 2013 | Volume 8 | Issue 10 | e75491
Some parameters that were shown to be correlated with the
performance during the 6MWT (such as customary physical
activity, smoking habits, socioeconomic status, depression, lower
cognition)  were not considered in our study. Although
important, however, these aspects were beyond our goals.
Finally, we did not consider in our study the relationship
between the 6MWD and parity, an interesting factor in developing
nations (4.3 in North Africa and 1.6 in Europe and North
America). It seems that parity accelerates decline of the 6MWD
. Although in our sample only Caucasian subjects were
enrolled, as in Italy there is a large number of immigrant, this
association should be evaluated in future studies.
In conclusion, the 6MWD by obese subjects is not only
influenced by age, sex and height, as reported in the majority of
reference equations in the extant literature. Disability should be a
pivotal variable of the predictive model of the distance walked by
obese subjects at the 6MWT.
Conceived and designed the experiments: LMD. Performed the experi-
ments: VM EP. Analyzed the data: AP AB LMD. Wrote the paper: LMD
1. Capodaglio P, Vismara L, Menegoni F, Baccalaro G, Galli M, et al. (2009)
Strength characterization of knee flexor and extensor muscles in Prader-Willi
and obese patients. BMC Musculoskelet Disord 10:47 doi: 10.1186/1471-2474-
2. Salvadori A, Fanari P, Mazza P, Agosti R, Longhini E (1992) Work capacity and
cardiopulmonary adaptation of the obese subject during exercise testing. Chest
3. Salvadori A, Fanari P, Fontana M, Buontempi L, Saezza A, et al. (1999) Oxygen
uptake and cardiac performance in obese and normal subjects during exercise.
4. Malatesta D, Vismara L, Menegoni F, Galli M, Romei M, et al. (2009)
Mechanical external work and recovery at preferred walking speed in obese
subjects. Med Sci Sports Exerc 41:426–434.
5. Wearing SC, Hennig EM, Byrne NM, Steele JR, Hills AP (2006) Musculoskel-
etal disorders associated with obesity: a biomechanical perspective. Obes Rev
6. Wearing SC, Hennig EM, Byrne NM, Steele JR, Hills AP (2006) The
biomechanics of restricted movement in adult obesity. Obes Rev 7:13–24.
7. Capodaglio P, Castelnuovo G, Brunani A, Vismara L, Villa V, et al. (2010)
Functional limitations and occupational issues in obesity: a review. Int J Occup
Saf Ergon 16:507–523.
8. Hulens M, Vansant G, Claessens AL, Lysens R, Muls E (2003) Predictors of 6-
minute walk test results in lean, obese and morbidly obese women. Scand J Med
Sci Sports 13:98–105.
9. Enright PL, Sherrill DL (1998) Reference equations for the six-minute walk in
healthy adults. Am J Respir Crit Care Med 158:1384–1387.
10. Troosters T, Gosselink R, Decramer M (1999) Six minute walking distance in
healthy elderly subjects. Eur Respir J 14:270–274.
11. Chetta A, Zanini A, Pisi G, Aiello M, Tzani P, et al. (2006) Reference values for
the 6-min walk test in healthy subjects 20-50 years old. Respir Med 100:1573–
12. Gibbons WJ, Fruchter N, Sloan S, Levy RD (2001) Reference values for a
multiple repetition 6-minute walk test in healthy adults older than 20 years.
J Cardiopulm Rehabil 21:87–93.
13. Ben Saad H, Prefaut C, Tabka Z, Mtir AH, Chemit M, et al. (2009) 6-minute
walk distance in healthy North Africans older than 40 years: influence of parity.
Respir Med 103: 74–84.
14. Enright PL, McBurnie MA, Bittner V, Tracy RP, McNamara R, et al. (2003)
The 6-min walk test: a quick measure of functional status in elderly adults. Chest
15. Li AM, Yin J, Au JT, So HK, Tsang T, et al. (2007) Standard reference for the
six-minute-walk test in healthy children aged 7 to 16 years. Am J Respir Crit
Care Med 176: 174–80.
16. Dourado VZ (2011) Reference Equations for the six-minute walk test in healthy
individuals. Arq Bras Cardiol 96:e128–e138.
17. Beriault K, Carpentier AC, Gagnon C, Me ´nard J, Baillargeon JP, et al. (2009)
Reproducibility of the 6-minute walk test in obese adults. Int J Sports Med
18. Capodaglio P, De Souza SA, Parisio C, Precilios H, Vismara L, et al. (2013)
Reference values for the six-minute walk test in obese subjects. Disabil Rehabil
19. Larsson UE, Reynisdottir S (2008) The six-minute walk test in outpatients with
obesity: reproducibility and known group validity. Physiother Res Int 13:84–93.
20. Donini LM, Brunani A, Sirtori A, Savina C, Tempera S, et al. (2011) SIO-
SISDCA task force: assessing disability in morbidly obese individuals: the Italian
Society of Obesity test for obesity-related disabilities. Disabil Rehabil 33:2509–
21. Precilios H, Brunani A, Cimolin V, Tacchini E, Donini LM, et al. (2013)
Measuring changes after multidisciplinary rehabilitation of obese individuals.
J Endocrinol Invest 36:72–7.
22. Capodaglio P, Cimolin V, Tacchini E, Precilios H, Brunani A (2013)
Effectiveness of in-patient rehabilitation in obesity-related orthopedic conditions.
J Endocrinol Invest Mar 19.
23. American Thoracic Society Statement: guidelines for the six-minute walk test
(2002) Am J Respir Crit Care Med 166:111–117.
24. Lohman TG, Roche AF, Martorell editors (1988) Anthropometric standardi-
zation reference manual. Human Kinetics Book, Champaign (IL – USA) 183.
25. Kushner RF (1992) Bioelectrical impedance analysis: a review of principles and
applications. J Am Coll Nutr 11:199–209.
26. Sun SS, Chumlea WC, Heymsfield SB, Lukashi HC, Schoeller D, et al. (2003)
Development of bioelectrical impedance analysis prediction equations for body
composition with the use of a multicomponent model for use in epidemiological
surveys. Am J Clin Nutr 77:331–340.
27. Andrews AW, Thomas MW, Bohannon RW (1996) Normative values for
isometric muscle force measurements obtained with hand-held dynamometers.
Phys Ther 76:248–259.
28. Borg G (1990) Psychophysical scaling with applications in physical work and the
perception of exertion. Scand J Work Environ Health 16 (Suppl 1):55–8.
29. Alameri H, Al-Majed S, Al-Howaikan A (2009) Six-minute walk test in a healthy
adult Arab population. Respir Med 103:1041–1046.
30. Enright PL (2003) The six minute walk test. Respir Care 48: 783–5.
31. Gosselink R, Troosters T, Decramer M (1996) Peripheral muscle weakness
contributes to exercise limitation in COPD. Am J Respir Crit Care Med 153:
32. Dourado VZ, Antunes LC, Tanni SE, de Paiva SA, Padovani CR, et al. (2006)
Relationship of upper-limb and thoracic muscle strength to 6-min walk distance
in COPD patients. Chest 129: 551–7.
33. Launois C, Barbe C, Bertin E, Nardi J, Perotin JM, et al. (2012) The modified
medical research council scale for the assessment of dyspnea in daily living in
obesity: a pilot study. BMC Pulmonary Medicine 12:61.
34. Camarri B, Eastwood PR, Cecins NM, Thompson PJ, Jenkins S (2006) Six
minute walk distance in healthy subjects aged 55–75 years. Resp Med 100:658–
35. Jenkins KR (2004) Obesity’s effects on the onset of functional impairment
among older adults. Gerontologist 44:206–16.
36. Jenkins S, Cecins N (2009) Regression equations to predict 6-minute walk
distance in middle-aged and elderly adults. Physiother Theory Pract 25:516–
37. Poh H, Eastwood PR, Cecins NM, Ho KT, Jenkins SC (2006) Six-minute walk
distance in healthy Singaporean adults cannot be predicted using reference
equations derived from Caucasian populations. Respirology 11:211–216.
38. Miyamoto S, Nagaya N, Satoh T, Kyotani S, Sakamaki F, et al. (2000) Clinical
correlates and prognostic significance of six-minute walk test in patients with the
primary pulmonary hypertension. Comparison with cardiopulmonary exercise
testing. Am J Respir Crit Care Med 161:487–492.
6-Minute Walking Distance in Obese Subjects
PLOS ONE | www.plosone.org7 October 2013 | Volume 8 | Issue 10 | e75491