Cigarette smoking is among the most common causes of COPD, as demonstrated in mice exposed to cigarette smoke daily for 8 weeks, whereby a 157% increase in serum tumor necrosis factor (TNF)-α, accompanied by significant decreases in the levels of peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) mRNA within soleus and extensor digitorum longus muscles were observed [18]. This evidence concerns the gene TNF and chronic obstructive pulmonary disease.