Changes of mitochondria volume density (Vv) (A), ratio of membrane area (δm) (B) and specific surface area (δ) (C) in intercostal, quadriceps, biceps and soleus muscles in control or chronic obstructive pulmonary disease rats treated with normal saline, Bufei Jianpi granules or aminophylline. Vv, δm is positive correlated to the function of mitochondria. δ is negative correlated to the activity of mitochondria. N = 6. *P < 0.05.