Smoking-induced skeletal muscle dysfunction: from evidence to mechanisms.

Smoking is the most important risk factor for the development of chronic obstructive pulmonary disease (COPD). Patients with COPD commonly suffer from skeletal muscle dysfunction, and it has been suggested that cigarette smoke exposure contributes to the development of skeletal muscle dysfunction even before overt pulmonary pathology. This review summarizes the evidence that muscles of nonsymptomatic smokers are weaker and less fatigue resistant than those of nonsmokers. Although physical inactivity of many smokers contributes to some alterations observed in skeletal muscle, exposure to cigarette smoke per se can also induce skeletal muscle dysfunction. Cigarette smoke constituents and systemic inflammatory mediators enhance proteolysis and inhibit protein synthesis, leading to loss of muscle mass. Reduced skeletal muscle contractile endurance in smokers may result from impaired oxygen delivery to the mitochondria and ability of the mitochondria to generate ATP due to interaction of carbon monoxide with hemoglobin, myoglobin, and components of the respiratory chain. Besides hampering contractile function, smoking may have immediate beneficial effects on motor skills, which are attributable to nicotine. In contrast to pulmonary pathology, many of the effects of smoking on skeletal muscle are most likely reversible by smoking cessation.