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

Changes in pressure pain thresholds (Measure of exercise-induced hypoalgesia)

Pressure pain thresholds (PPT) will be assessed at the wrist and patella. PPT being assessed at a remote body site (e.g., wrist) is to measure central pain sensitivity while PPT being assessed at the location of pain (i.e., knee, patellae) is to assess peripheral pain sensitivity with or without central pain sensitivity. PPT will be assessed using a handheld pressure algometer with 1 cm2 rubber tip. PPT will be defined as the point at which the participant verbally indicated that the pressure first changed to slight pain. A lower PPT value (Kgf) represents greater pain sensitivity. PPT will be assessed 3 times at each location and averaged. Furthermore, changes in PPT after exercise has been used to assess the degree of exercise-induced hypoalgesia (EIH). When PPT values increase after the exercise, it indicates a reduction of pain sensitivity and, therefore, an effect of EIH.

Mechanical temporal summation

Temporal summation (TS) is a sensitive measurement of central pain sensitivity. Investigators will assess TS using a standard set of weighted probes from 64-512 mN. Participants will rate the pain experienced by each successive weighted probe being touched on the skin of the wrist until a pain rating of ≥ 4/10 is achieved. The selected probe will be then applied at a frequency of 1 Hz for 10 seconds on the wrist. Participants will provide a pain rating at the completion of the train of 10 stimulations and 15 seconds post-stimulation. TS will be defined as the difference between the highest post-stimulation pain rating and the initial pain rating. A post-stimulation pain rating greater than the initial pain rating will be considered to be reflective of an increase in central pain sensitivity.

Conditioned pain modulation

Conditioned pain modulation (CPM) evaluates the adequacy of the descending pain modulatory pathways, which contributes to central pain sensitivity. Investigators will assess CPM using PPT as the test stimulus (PPT1) at the wrist as described above, with forearm ischemia using a blood pressure cuff as the conditioning stimulus. Briefly, the blood pressure cuff applied to the contralateral arm will be inflated to 10mm Hg above systolic pressure. The participant will be then instructed to perform hand grip squeezes until pain of at least 4/10 occurs in the contralateral arm. PPT will be then reassessed at the wrist 3 times and averaged (PPT2). Percent efficiency of CPM (%CPM) was computed as PPT2/PPT1, multiplied by 100; %CPM ≤ 100 indicates inefficient CPM.

Knee pain

We will assess changes in knee pain with a 20 meter walk using a 0-10 numeric rating scale where 0 indicates no knee pain and 10 indicates the worst knee pain.

Racial discrimination

Racial discrimination will be assessed with the Perceived Experiences of Discrimination Questionnaire-Community Version (PEDQ-CV). This is a reliable and valid 17-item survey that assesses experiences of racialized discrimination.

Acculturative Stress

Acculturative stress will be assessed with The Social, Attitudinal, Familial, Environment Acculturative Stress Scale (SAFE). SAFE is composed of 24 items that measure stress as a result of the acculturation process in four contexts: social, attitudinal, familial and environmental acculturative.

Autonomic function

Heart rate variability (HRV), a measurement of autonomic function, will be assessed using a wearable and wireless heart rate monitor. Investigators will have participants lie supine for 5 minutes to collect heart rate variability parameters such as high frequency and high-frequency/low-frequency ratio.

The Western Ontario McMaster Universities Osteoarthritis Index (WOMAC)

WOMAC knee pain scale ranges 0-20 with 5 questions assessing knee pain in different contexts such as knee pain during walking and pain during standing. Each question has a score of 0-4. A greater WOMAC score represents greater knee pain.