The aim of this randomized controlled trial is to evaluate the effect of Nordic walking and inspiratory muscle training (IMT) on cardiopulmonary function in patients with knee osteoarthritis (OA). Mild-to-moderate knee OA patients are randomly allocated into Experimental group (Nordic walking plus routine management) or Control group (Routine management). While End-stage knee OA patients are randomly allocated into Experimental group (IMT plus pre-operative rehabilitation exercise) or Control group (Pre-operative rehabilitation exercise). Participants are invited to undergo two assessments, including baseline assessment, post-intervention assessment. Researchers will compare two groups to see if the cardiopulmonary function can be improved after intervention.

This study recruits patients with different stages and assigns them into different interventions and comparing the effect with those not receiving intervention. It will provide the evidence in terms of the exercise that can promote cardiopulmonary function and at the same time reduce pain and disability for patients with different stages of knee osteoarthritis.

Inclusion Criteria:

• pain on the most days in one or both knees in the past month;
• difficulty with at least one of daily living activities measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scale;
• radiographic evidence of knee OA in the tibial-femoral compartment (Kellgren and Lawrence grade, K/L ≥1, K/L 1-3 regarded as mild-to-moderate knee OA, others waiting for knee arthroplasty regarded as end-stage knee OA);
• with normal or corrected visual and auditory function and walking unaided;
• primary knee OA for more than 6 months, be stable on medication for at least 3 weeks.

Exclusion Criteria:

• knee surgery priorly;
• have steroid injection in previous three weeks;
• have inflammatory arthritis (e.g., rheumatoid); or unstable angina, or myocardial infarction, or cardiac surgery; or stroke; or treatment with steroids, hormones, or cancer chemotherapy; or pulmonary diseases (force vital capacity<80% of predicted and/or forced expiratory volume at first second<70% of predicted); or a history of exercise-induced asthma;
• unable to understand the procedure and potential risks of the study;
• medically unstable that indicate unsafe to participate in exercise test

There is no plan to make individual participant data available to other researchers.

Investigator and outcomes assessor won't know the allocation of participants.