This study is to determine how 8-week Tai Chi intervention alters plasma endocannabinoid and its receptors in monocytes/marcrophages, plasma oxylipinds, plasma brain-derived neurotrophic factor, brain white matter connectivity/efficiency, and functional/clinical outcomes in women with knee OA.

Knee osteoarthritis (OA) is one of the five leading causes of disability. Previous studies have shown that a mind-body moderate-intensity Tai Chi (TC) exercise (8-24 weeks) reduced pain and improved physical function for knee OA, when compared to a waiting list, attention control, usual physical activity, or physical therapy. However, TC's mechanisms of action regarding improvement of one's clinical condition and its functional outcomes in individuals with knee OA are poorly understood. This study is to determine how 8-week TC intervention alters plasma endocannabinoid and its receptors in monocytes/marcrophages, plasma oxylipinds, plasma brain-derived neurotrophic factor, brain white matter connectivity/efficiency, and functional/clinical outcomes in women with knee OA.

Inclusion Criteria:

1. Postmenopausal women.
2. WOMAC pain score ≥ 50 on at least 1 of the 5 questions in pain subscale (range of 0 to 100, with higher scores indicating greater pain.
3. English literacy.
4. Able to undergo an MRI scan
5. Diagnosed Have the following symptoms associated with knee OA based on American College of Rheumatology clinical classification criteria for osteoarthritis (Peat 2006). Pain in the knee. Need to at least 3 of the following: over 50 years of age, less than 30 minutes of morning stiffness, crepitus on active motion, bony tenderness, bony enlargement, or no palpable warmth of synovium.

Exclusion Criteria:

1. Prior experience with mind-body practice (e.g. TC, Qi Gong, yoga, or acupuncture) or physical therapy programs for knee OA within the past 3 months.
2. Severe medical limitations (i.e., dementia, symptomatic heart or vascular disease, or recent stroke) precluding full participation.
3. Medical/neurologic or other systemic diseases affecting the musculoskeletal systems (i.e. polio/Parkinson's/multiple sclerosis, etc. in addition to cerebral vascular accident or stroke) and diabetes with peripheral neuropathy affecting their sensory/balance.
4. Intra-articular steroid injection or reconstructive surgery on most severely affected knee in the past three months.
5. Intra-articular hyaluronic acid injections on most severely affected knee in the past six months.
6. Inability to walk without an assistive device.

Postmenopausal women.