This is a single center, randomized, double-blind, placebo controlled clinical trial.
Eligibility criteria:
1. moderate-to-severe COPD patients
2. aged 40-80 years,
3. abstaining from cigarette smoking or maintaining a stable dose of cigarette consumption,
4. no acute exacerbation of COPD,
5. clinically being stable for one month and longer,
6. not undergoing exercise training program.
Primary endpoint:
six-minute walk distance in meters at week 12.
