Many respiratory diseases lead to impaired function of skeletal muscles, influencing quality of life and patient survival. Dysfunction of both respiratory and limb muscles in chronic obstructive pulmonary disease has been studied in depth, and seems to be caused by the complex interaction of general (inflammation, impaired gas exchange, malnutrition, comorbidity, drugs) and local factors (changes in respiratory mechanics and muscle activity, and molecular events). Some of these factors are also present in cystic fibrosis and asthma. In obstructive sleep apnea syndrome, repeated exposure to hypoxia and the absence of reparative rest are believed to be the main causes of muscle dysfunction. Deconditioning appears to be crucial for the functional impairment observed in scoliosis. Finally, cachexia seems to be the main mechanism of muscle dysfunction in advanced lung cancer. A multidimensional therapeutic approach is recommended, including pulmonary rehabilitation, an adequate level of physical activity, ventilatory support and nutritional interventions.