Persistent airflow limitation characterizes individuals with chronic obstructive pulmonary disease (COPD), resulting in symptoms such as dyspnea and fatigue. The association with reduced physical activity levels leads to worsening of the symptoms and characterizes a “vicious circle”, which is related to the appearance of multiple extrapulmonary effects.1–3

The American College of Sports Medicine (ACSM) and the American Heart Association (AHA) recommend a minimum of 30min of physical activity of moderate intensity (5 times per week) or 20min of physical activity of vigorous intensity (at least 3 times/week) for an individual to be considered physically active; or even, to accumulate 3 bouts or more of 10min of vigorous intensity.4,5 Those individuals who do not reach these recommendations are considered physically inactive, and it is known that inactivity contributes to the increase of exacerbations’ frequency and morbimortality in people with COPD.6

Individuals with COPD often present metabolic dysfunctions that may influence their body composition.7,8 Furthermore, body composition abnormalities, may lead to impaired exercise capacity, more severe dyspnea and fatigue, worse health status, and higher mortality rate.7,9–12 Sarcopenia is a body composition abnormality characterized by low fat-free mass index (FFMI), and this condition is associated with decreased physical activity in daily life (PADL), functional performance, and exercise capacity.13,14 Obesity, another possible body composition abnormality, is also associated with decreased PADL, worse exercise capacity, and impaired lung function in individuals with COPD.15,16 However, due to the “protective effect” present in the obesity paradox, obese individuals with COPD may present better disease prognosis than those with normal body mass index (BMI).8,17,18 On the other hand, the combination of obesity and sarcopenia in this population is related to worse physical performance compared to other body composition phenotypes.19,20

Despite the array of important clinical complications involved, the phenotype profiling of individuals with COPD according to body composition abnormalities and the level of PADL has never been studied, and the present study focuses on the potential clinical implications of these phenotypes by hypothesizing that the combination of abnormalities in body composition and physical inactivity may further impair the physical functional characteristics of this population. Therefore, the aim of this study was to determine if individuals with COPD classified as physically active or inactive present different physical functional characteristics within different body composition phenotypes.

A retrospective analysis was undertaken using available baseline-only data from a convenience sample of 176 individuals with COPD assessed during an initial evaluation at the Pulmonary Rehabilitation program at the University Hospital of Londrina (HUL, Brazil). The present sample combines participants from a previously published study21 with those from an ongoing study (ClinicalTrials.gov number, NCT03127878), and all data were collected in the period of pre-rehabilitation assessments between 2006 and 2019. Both studies were approved by the Research Ethics Committee from the Universidade Estadual de Londrina, Paraná, Brazil (nos. 123/09 and 1.730.247) and all participants signed an informed consent form.

Inclusion criteria were the same as those for the two above mentioned related studies: COPD diagnosis according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria2; absence of any regular physical training in the preceding year; clinical stability defined as absence of exacerbations within the last month; and absence of severe comorbidities that could interfere in the assessment protocol (e.g. orthopedic, rheumatological, neurological, or cardiovascular conditions). Individuals were excluded from the present study's analyses in case of missing (unavailable) data concerning the complete assessments of body composition and PADL.

One hundred and seventy six individuals with COPD, with mean age of 67±7.9 years and moderate to very-severe airflow obstruction (47.0±16.2%pred) were included. According to physical activity, the participants had a low PADL level (30.3 [10.3–70.8] min/day of MVPA) and relatively high sedentary time (444±118.5min/day of activities <1.5 MET) as shown in Table 1. Individuals were classified as NBC+Act (17%), NBC+Inact (21.6%), Ob+Act (6.3%), Ob+Inact (9.7%), Sarc+Act (12.5%), Sarc+Inact (8.5%), Sarc/Ob+Act (8.0%) and Sarc/Ob+Inact (16.5%).

Table 2 shows that the Sarc/Ob+Inact group presented lower 6MWT in % of the predicted value and 1RM for knee extension in comparison to NBC+Act, NBC+Inact, and Ob+Act groups and lower 6MWT in meters in comparison to the Ob+Act and Sarc+Act groups (p<0.05 for all). The Sarc/Ob+Inact group also presented lower FEV1, 1RM elbow flexion and elbow extension in comparison to NBC+Act and NBC+Inact groups, and lower 1RM for elbow extension compared to the Ob+Inact group (p<0.05 for all), in addition to a near-significance for lower 1RM for elbow flexion compared to the Ob+Act group (p=0.07). Although there were no statistically significant differences for MRC, LCADL, and HADS, some between-groups MIDs were reached in these instruments’ scores (Table 2).

There was significant effect of body composition and PADL level on the 6MWT%pred (p=0.004 and p=0.008, respectively), as well as on the 1RM for elbow flexion (p=0.001 and p=0.04, respectively). As for the 1RM for knee extension, body composition presented a significant effect (p=0.01), and PADL level presented a near-significant effect (p=0.09).

The present study investigated whether individuals with COPD classified as active or inactive present different physical and functional characteristics within different body composition phenotypes and its results showed that worse exercise capacity, muscle force, and lung function are found when physical inactivity is added to the combination of sarcopenia and obesity. Moreover, while benefits of being physically active in this population are well-established in the literature, the present study suggests that individuals with a profile of physical inactivity added to body composition abnormalities should be seen as primary therapeutic targets. These results are consistent with those from Machado et al.20 who showed that individuals classified as sarcopenic/obese were most debilitated, considering their worse exercise capacity, PADL, and peripheral and respiratory muscle strength.

The novelty of adding the burden of physical inactivity to the body composition phenotype of sarcopenia and obesity highlights the importance of the physical activity level in this population. In contrast to the Sarc/Ob+Inact group, obese and sarcopenic individuals showed no differences in any outcome when compared to the NBC group, regardless of PADL level. To counteract inactivity, some “strategies” are known, such as having an active partner, going out to walk the dog, playing with grandchildren, and participating in behavior change coaching activities, among others.41–43

Poulain et al.44 previously showed that obese individuals with COPD are characterized by a higher FFM. This observation is important because, as already shown in previous studies, muscle mass predicts survival better than BMI.7,12,45 Moreover, exercise capacity is also a strong predictor of survival in individuals with COPD.46 Individuals with COPD who are obese appear to present with an advantage due to “obesity paradox”, that is associated with higher survival and functional outcomes, but in contrast also associated with increased risk of metabolic and cardiovascular disease.47 Groups Ob+Act and Sarc+Act had better exercise capacity than Sarc/Ob+Inact, and this is consistent with previous studies that showed a relationship between FFM and exercise capacity, as a negative energy balance (e.g. loss of muscle mass) may affect the individual's tolerance to exercise.14,19,47

There were no significant differences in MRC scores among groups possibly due to the fact that all groups presented median score of 3 or 4, therefore all of them fitting in the most impaired groups of the GOLD classification.2 As for the LCADL, there were also no significant differences among groups, although some of them presented differences greater than the MID of 3 points; this may indicate differences in functional limitation among them, despite the lack of statistical significance.38 For the HADS, although differences greater than the MID of 1.5 points,40 was present between some groups, these individuals were unlikely severely affected by anxiety and depression, because the scores were generally relatively low.

One of the novelties and strengths of the present study is that it is the first to our knowledge in the scientific literature to analyze differences in clinical features of individuals with COPD classified according to their body composition phenotypes and level of physical (in)activity. The clinical implication of the present results is that individuals combining sarcopenia and obesity with inactivity need more attention from health professionals. Furthermore, another strength of the study is that the accelerometer used to assess PADL is valid and accurate specifically for individuals with COPD,24–27 a population known to be mostly inactive, sedentary, and composed of slow-walking individuals.

Some study limitations to take into account were: the cross-sectional design (not allowing to infer causality); the results cannot be extended to individuals classified as GOLD I, because our sample had only one individual in this category; the reference values for FMI and FFMI, as well as the formula used to estimate FFM, were not developed specifically for the Brazilian population; the PADL assessment being performed over only two days, while sufficient for reliable measurements in more severe individuals, may require more days in individuals with milder impairment28,48; and the unavailability of important information to describe the sample of participants, such as information on socioeconomic status, educational level, and climatic conditions during the PADL assessment. Lastly, the use of bioelectrical impedance may present limitations related to hydroelectrolytic abnormalities and the choice of the appropriate population, age, or disease-specific equations.49

Moreover, new and interesting scientific possibilities may unfold from the present results. Future studies should investigate whether increasing PADL level, associated or not with changes in body composition phenotypes, at least in borderline individuals, may result in improvements in physical function of individuals with COPD.

Worse exercise capacity, muscle force, and lung function are found when physical inactivity is added to the combination of sarcopenia and obesity in individuals with moderate to very severe COPD.

The authors declare no conflicts of interest.