Chronic obstructive pulmonary disease (COPD) is characterized by irreversible airway obstruction and progressive deterioration of respiratory function. Patients with COPD show a limited exercise tolerance, early fatigability and progressive dyspnea, with important consequences on the ability to sustain even mild efforts and a drastic restriction in the activities of daily living. Muscle dysfunction is a systemic manifestation of COPD that contributes to exertion intolerance in individuals with COPD to the point of compromising fundamental functional activities, such as walking. Previous studies have shown, in fact, that quadriceps strength can be reduced by 20% to 30% in patients with COPD and this value is associated with an increased risk of mortality in patients with lower strength levels. In addition, loss of muscle mass or sarcopenia also occurs with a prevalence of between 8% and 67% in patients with COPD, exacerbating the picture of muscle dysfunction.

One of the goals of respiratory rehabilitation is precisely the prevention of muscle dysfunction in patients with COPD. However, rehabilitation programs aimed at maintaining and recovering muscle strength are often lacking in guidance regarding target muscles, duration of sessions, and training intensity, while strength assessment is often limited by the timing and resources associated with the clinical setting in which it takes place. This makes it difficult to determine its short- and long-term effectiveness.

Therefore, assessment of muscle function in patients with COPD requires tests that are simple and quick to perform, but equally capable of providing quantitative data referable to a specific characteristic of muscle strength as well as indicative of the patient's overall function. In addition, complementary measurements such as body composition and muscle mass, as well as the development of predictive models and normative values of muscle function could provide additional information on the progression of muscle dysfunction in patients with COPD, allowing rehabilitation intervention to be directed toward recovery of the most compromised functions.

Therefore, the aims of this study are: 1) To evaluate the effectiveness of a standard pulmonary rehabilitation program in recovering peripheral muscle dysfunction in patients with COPD. 2) To evaluate the clinical reliability of tests commonly used to measure peripheral muscle function in the rehabilitation setting of patients with COPD.

Inclusion Criteria:

• COPD diagnosis (GOLD stage: II-III-IV), defined as post-bronchodilator forced expiratory volume in 1s (FEV1)/forced vital capacity < 0.7 and FEV1 < 80% predicted.

Exclusion Criteria:

• Restrictive lung disease, unstable conditions, recent exacerbation, infection, embolism, pneumothorax, thoracic or abdominal surgery (less than 3 months before recruitment).
• Cardiologic conditions like myocardial infarction (less than 6 months before recruitment), heart failure, or severe angina.
• Inability of perform the exercise training (e.g. orthopaedic conditions).
• Incapability to understand the instructions required to carry out the tests and assessments planned.

Outpatients with COPD referred to the Cardiopulmonary Rehabilitation Unit of a tertiary referral sub-acute rehabilitation centre.