Chronic obstructive pulmonary disease (COPD) is a progressive and heterogeneous disorder characterized by persistent airflow limitation and systemic manifestations that substantially impair quality of life and survival. Although tobacco smoke exposure remains the dominant etiological determinant, COPD is increasingly recognized as a complex multisystem disease in which extrapulmonary alterations, including systemic inflammation and skeletal muscle dysfunction, contribute to functional decline and adverse outcomes 1. For decades, physical inactivity has been interpreted primarily as a downstream consequence of dyspnea, fatigue, deconditioning, and exacerbation burden. However, a growing body of evidence supports a more clinically relevant paradigm, namely that physical inactivity is not merely an epiphenomenon of COPD severity but represents a modifiable behavioral exposure that may meaningfully contribute to disease progression. This view is supported by consistent prognostic evidence showing that low daily physical activity is associated with a higher risk of hospitalization, exacerbations, and mortality, even after adjustment for traditional indices of disease severity 2. Interestingly, these associations are not restricted only to advanced disease. Reduced daily physical activity is already evident in earlier COPD stages 3, suggesting that inactivity may emerge early and confirming that it may not be fully explained by airflow limitation alone. It is important to emphasize that physical activity should not be confused with exercise capacity. Physical activity reflects what patients actually do in daily life, whereas exercise capacity reflects what they can do under standardized testing conditions. This distinction is clinically relevant because daily activity is strongly influenced by behavioral, psychological, and environmental determinants and cannot be reliably inferred from lung function or exercise tests alone 4. Accordingly, the clinical relevance of physical inactivity extends beyond performance-based physiological impairment, capturing a behavioral phenotype that may carry independent prognostic and mechanistic implications. From a longitudinal perspective, trajectories of daily activity are particularly informative. Patients who progressively shift toward a persistently inactive lifestyle experience the highest mortality risk, implying that declining daily activity reflects a broader systemic deterioration not fully explained by airflow limitation 5. Moreover, sedentary time may carry prognostic relevance even when some moderate-to-vigorous activity is preserved, supporting the need to consider the entire daily movement profile in COPD 4. These prognostic signals are consistent with a biologically plausible mechanistic framework, in which physical inactivity may amplify systemic and peripheral pathways already dysregulated in COPD (Figure 1). Physical activity modulates cytokine networks and immune pathways, contributing to a more favorable inflammatory profile 6. Conversely, prolonged inactivity is associated with higher circulating inflammatory biomarkers, including interleukin-6 and C-reactive protein, even independently of obesity 7. In COPD, systemic inflammation is sustained by smoke-related injury, exacerbation-related inflammatory bursts and, in many patients, chronic hypoxemia. In this setting, physical inactivity may further amplify inflammatory signaling and help maintain this systemic burden over time. This inflammatory background is closely linked to oxidative stress and mitochondrial dysfunction, which represent central biological pathways in inactivity-related deconditioning. Experimental and translational evidence indicates that muscle disuse rapidly increases reactive oxygen species generation and activates redox-sensitive signaling cascades that favor protein degradation and loss of muscle mass 8. Oxidative stress also contributes to impaired mitochondrial respiration and cellular dysfunction and has been proposed as an upstream signal activating proteolytic systems such as the ubiquitin-proteasome pathway. In COPD, these alterations overlap with disease-specific drivers of muscle dysfunction, suggesting that inactivity may reinforce a vicious cycle of redox imbalance, mitochondrial impairment, and progressive loss of muscle integrity 8. Skeletal muscle dysfunction is one of the most clinically relevant systemic manifestations of COPD and is strongly associated with reduced endurance, impaired exercise tolerance, disability, and mortality. The American Thoracic Society/European Respiratory Society statement emphasizes that limb muscle dysfunction is not a secondary complication but a core systemic component influencing prognosis and long-term outcomes 1. Physical inactivity likely acts as a key amplifier of these processes by promoting deconditioning, reducing oxidative capacity, shifting muscle metabolism toward glycolytic pathways, and accelerating the transition toward frailty. In this setting, muscle dysfunction becomes not only a consequence of reduced activity, but also a determinant of further inactivity, thereby consolidating progressive functional decline. Interestingly, physiological consequences extend beyond peripheral muscle impairment. Inactive individuals exhibit greater ventilatory inefficiency during exertion, a feature that has been described even in early COPD and is closely associated with exertional dyspnea 9. Deconditioning increases lactate production during low-intensity activity, raising ventilatory requirements and amplifying symptoms. As a result, even routine daily tasks may become disproportionately demanding, contributing to activity avoidance and reinforcing a self-perpetuating loop in which reduced daily movement progressively increases ventilatory demand and symptom burden 9. Physical inactivity also appears to influence exacerbation susceptibility, an outcome that is central to COPD progression. Patients with low daily physical activity levels experience a higher risk of hospitalization for acute exacerbations, and this association appears independent of baseline lung function impairment 2. Although causal pathways remain incompletely defined, systemic inflammation, impaired immune competence, respiratory muscle weakness, and reduced mucociliary clearance may collectively increase vulnerability to infectious triggers and environmental stressors. Exacerbations, in turn, cause abrupt declines in physical activity, leading to persistent deconditioning and accelerating functional deterioration. Beyond pulmonary outcomes, inactivity is also linked to higher cardiometabolic risk and contributes to the broader multimorbidity burden that characterizes COPD. This observation aligns with the broader physiological framework that the lack of exercise is a major determinant of chronic disease burden through integrated effects on inflammation, metabolic regulation, and systemic organ vulnerability 10. Within COPD populations, this may partly explain why inactivity predicts survival so consistently and so strongly. Taken together, these observations support a conceptual shift in COPD management. Physical inactivity should be considered a treatable behavioral trait and a plausible disease modifier, potentially acting as both a marker and mediator of COPD progression. From a clinical standpoint, objective monitoring of physical activity should be incorporated into routine assessment, and early identification of inactivity phenotypes may allow targeted interventions before irreversible disability develops 4. Pulmonary rehabilitation remains a cornerstone strategy, but sustaining long-term behavioral change remains challenging and deserves the same level of clinical attention as pharmacological escalation. In conclusion, physical inactivity is a pervasive and clinically meaningful feature of COPD that extends beyond functional limitation. Current evidence supports its role as a major contributor to systemic inflammation, oxidative stress, skeletal muscle dysfunction, ventilatory inefficiency, exacerbation susceptibility, and cardiometabolic burden. Accordingly, targeting inactivity should be regarded not as an adjunctive measure, but as a core component of disease-modifying strategies in COPD. This research was supported by the "Ricerca Corrente" funding scheme of the Italian Ministry of Health. The authors have nothing to report. M.M. reports grants or contracts from GlaxoSmithKline, AstraZeneca and Chiesi outside the submitted work. All other Authors declare no competing financial interests. Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.
Fuschillo et al. (Sun,) studied this question.