Upper and Lower Extremity Exercise and Exercise-Induced Hypoalgesia in Knee Osteoarthritis

Participants with knee OA (Target n=40)

Inclusion Criteria:

We will recruit participants with knee OA, using the National Institute for Health and Care Excellence's clinical diagnostic criteria, which does not require radiographs. The clinical diagnostic criteria include:

* age ≥45
* activity-related knee pain
* either no morning joint-related stiffness or stiffness that lasts ≤ 30 minutes.
* knee pain at least 4 on a 0-10 pain scale
* knee pain as a chief complaint if having multiple pain
* understand English

Exclusion Criteria:

* peripheral neuropathy or other sensation loss on the body sites for pain measurements (i.e., the wrist, knee, the forearm)
* use of medical devices electrically active (e.g., pacemaker)
* chronic use of opioids
* pregnant women
* serious and uncontrolled concomitant disease, including cardiovascular, nervous system, pulmonary, renal, hepatic, metabolic, hormonal, endocrine, gastrointestinal or epileptic disease
* rheumatoid arthritis, ankylosing spondylitis, and any neurological disorders that prevent the study procedure
* cognitive impairment
* history of a knee replacement surgery
* inability to perform exercise due to severe pain or other symptoms
* any intervention procedures for knee pain in the last 3 months

Inclusion and exclusion criteria for pain-free controls (Target n = 20) Pain-free controls are not having a pain-related medical condition. They have to speak and understand English. Pain-free controls are excluded if they had experienced a pain episode, caused by musculoskeletal injury or otherwise in the previous 3 months.