The goal of this clinical trial is to investigate whether an astaxanthin-based dietary supplement combined with a pulmonary rehabilitation training program could improve exercise capacity in patients with COPD. The main questions it aims to answer are:

• whether an astaxanthin-based dietary supplement combined with a pulmonary rehabilitation training program could improve 6MWD in patients with COPD.

The drug administration group will receive:

• Two capsules of astaxanthin formula supplement daily for 8 weeks.
• Pulmonary rehabilitation training: a total of 8 weeks, 2-3 times a week.

The control group will receive a total of 8-week pulmonary rehabilitation training, 2-3 times a week.

The investigators will compare the drug administration group and the control group to see if the difference between the 2 groups reaches a minimal clinically important difference.

Inclusion Criteria:

• Patients who met the GOLD diagnostic criteria for stage II-IV COPD

• Patients who met the indications for pulmonary rehabilitation training: mMRC score

  • 3 or self-reported decline in physical function.

Exclusion Criteria:

• Hypoxemia (resting partial pressure of oxygen < 60mmHg or oxygen saturation < 88%) or patients requiring continuous oxygen therapy or with any contraindications to exercise testing (refer to the American Society of Thoracic Surgeons/American College of Chest Physicians exercise testing guidelines).
• Using oral glucocorticoids
• Long-term oxygen therapy
• Participated in a supervised exercise program within the past 12 months
• History of other pulmonary diseases, including pneumoconiosis, bronchiectasis, tuberculosis, primary pulmonary hypertension, pulmonary embolism, interstitial lung disease
• Skeletal, neuromuscular, cardiovascular, or metabolic disorders that limit the participant's ability to exercise actively or that involve muscle activity, such as cancer, diabetes, muscle weakness, etc.