75 Review www.expert-reviews.com © 2012 Expert Reviews Ltd ISSN 1747-6348 10.1586/ERS.11.81 Any impairment in striated muscle function can interfere with the performance of daily activities, particularly for a patient already liv- ing with a respiratory disorder. However, the interaction between the respiratory and mus- culoskeletal systems is not always considered in the clinical management of these patients. Striated muscles are contractile elements that provide organisms with physiological func- tions, such as movement and generation of both air- and blood-flow. The latter two func- tions are essential for respiratory gas exchange. The generation of airflow requires the action of inspiratory muscles. When this muscle group contracts, the changes in intrathoracic pres- sure allow air to enter the lungs. When these muscles relax, the air exits from the respira- tory system. If additional effort is required to exhale, the expiratory muscle group contracts, increasing the alveolar–atmosphere pressure gradient. Although the diaphragm is the main inspiratory muscle, specifically in young and healthy subjects when they are at rest, other muscles progressively participate in the effort as ventilatory demands increase. These include external intercostals, parasternal and, to a lesser degree, the scalenes, sternocleidomas- toid, latissimus dorsi, serratus and pectoralis muscles. The main expiratory muscles are the internal intercostals and those constituting the abdominal wall. Skeletal muscles located in the limbs (and also called peripheral muscles), are involved in the movements of the body. Any impairment in their function can interfere with the performance of daily activities. Muscle function becomes impaired in many different respiratory disorders, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis, bronchial asthma, obstructive sleep apnea syndrome (OSAS), kyphoscoliosis and lung cancer. Although changes in respiratory mechanics in these diseases primarily target respiratory muscles, limb muscles can also be affected. In addition, respiratory and limb muscle dysfunction can occur in patients with myopathies, neurological and neuromuscular junction disorders, chronic heart failure, sepsis and other critical illness. In the intensive care unit (ICU), the condition called ICU muscle weakness is not only a limb problem but can also hamper weaning from mechanical ventilation. This review aims to briefly present basic concepts of skeletal muscle physiology and to describe in-depth the muscle function impair- ment occurring in some of the most prevalent respiratory conditions, defining the factors and mechanisms involved in the etiopathogenesis of muscle dysfunction in this setting. Joaquim Gea*, Carme Casadevall, Sergi Pascual, Mauricio Orozco-Levi and Esther Barreiro Servei de Pneumologia, Hospital del Mar – IMIM, Departament de Ciències Experimentals i de la Salut (CEXS), Universitat Pompeu Fabra, CIBER de Enfermedades Respiratorias (CIBERES) ISC III, Barcelona, Catalunya, Spain *Author for correspondence: Tel.: +34 93 248 3138 Fax: +34 93 248 3425 jgea@parcdesalutmar.cat 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. KEYWORDS:฀drugs฀•฀exercise฀limitation฀–฀muscle฀remodeling฀•฀hypoventilation฀•฀infammation฀•฀limb฀muscles฀ •฀muscle฀dysfunction฀•฀respiratory฀diseases฀•฀respiratory฀muscles Respiratory diseases and muscle dysfunction Expert Rev. Respir. Med. 6(1),฀75–90฀(2012) For reprint orders, please contact reprints@expert-reviews.com