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

The objective of the study is to explore the effects of arm exercise (UE, arm ergometer) vs. leg exercise (LE, cycling ergometer) on exercise-induced hypoalgesia (EIH), central pain mechanisms and knee pain in people with knee osteoarthritis (OA). Furthermore, we will explore relations of socioeconomic status, racial discrimination, acculturative stress, and autonomic function to exercise effects on EIH, central pain mechanisms, and knee pain. This will be a pilot randomized cross-over study where all participants undergo Day 1 (baseline assessments), Day 2 (UE or LE), and Day 3 (UE or LE).

This will be a pilot randomized cross-over study. Major exclusion criteria will be conditions that have risks with exercise or affect pain assessments. Once enrolled, all participants will undergo 3 laboratory visits, each separated at least by a week as a wash-out period: day 1, baseline assessment; day 2, randomized to either upper extremity exercise (UEE) (i.e., arm ergometer) or knee exercise (KE) (i.e., cycling ergometer); and day 3, UEE or KE alternative to the exercise on day 2. UEE will be an arm-ergometer and KE will be a cycle-ergometer in which participants will undergo the first 5 minutes at an intensity of 50% heart rate reserve (HRR)(warm-up period), followed by 20 minutes at 70% HRR. Heart rate will be monitored during the exercise.

On day 1, we will collect participant characteristics data. We will also collect data related to race/ethnicity, racial discrimination, acculturative stress, physical activity level, heart rate variability (HRV) parameters (measures of autonomic function). Further, participants will undergo knee pain assessment with a 20-meter walk, quantitative sensory testing (QST) measures of pressure pain threshold (PPT), temporal summation (TS), and conditioned pain modulation (CPM) as surrogate measures of central pain mechanisms.

On Days 2 and 3 we will collect knee pain, QST, and EIH data before and immediately after the exercise.

Eligibility Criteria:
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.