Our goal is to compare the serum biomarker changes of joint disease that occur in response to partially off-loaded (50%) walking exercise to regular (100%) walking exercise while on a Lower Body Positive Pressure (LBPP) treadmill. Secondly we are determining the relationship between changes in the concentration of these serum biomarkers and participant reported knee pain while walking on a LBPP treadmill.

The morphology and composition of healthy mature articular cartilage is optimized to its primary function of load transfer and distribution. In the osteoarthritic state however, homeostasis of the knee joint is significantly altered, such that as load is placed on the joint there is progressive worsening of cartilage damage over time. Altered joint mechanics and intra-articular biological processes are thought to play pivotal roles in the initial breakdown and potentiation of cartilage damage which is the hallmark finding in knee OA leading to knee pain. Walking or running with weight support on a lower-body positive-pressure (LBPP) treadmill is a novel training and rehabilitation modality for individuals with lower extremity pathologies due to its ability to limit pain. This treadmill provides a controlled off-loading of the lower extremities with significant benefit being shown after 12 weeks of training in overweight individuals with knee OA on knee pain, function and muscle strength. Although this methodology alters the joint mechanics, the intra-articular biological effect on joint disease remains unknown.

A recent study from our laboratory compared walking exercise on a regular treadmill at a defined speed with and without rest breaks in 27 participants with knee OA and demonstrated that one-hour rest breaks had significant benefits. This conclusion was based on reduction in knee joint contact force and decreased levels of a serum marker commonly associated with cartilage degradation (cartilage oligomeric matrix protein, COMP) at 45 minutes of walking. This investigation assessed patterns of walking, but the impact of varying knee joint contact force, such as by walking on a LBPP treadmill on the biological profiles of joint disease is not known. The present study will establish the conditions and parameters for a future longer-term clinical trial that aims to individualize the amount of joint loading during LBPP treadmill training in participants with knee OA based on their biomarker profile.

Objective 1: Compare the serum biomarker changes of joint disease that occur in response to partially off-loaded (50%) walking exercise to regular (100%) walking exercise while on a LBPP treadmill.

Objective 2: Determine the relationship between changes in the concentration of these serum biomarkers and participant reported knee pain while walking on a LBPP treadmill.

Inclusion Criteria:

• Age > 50 years
• Diagnosis of unilateral or bilateral knee osteoarthritis
• Clinical AND/OR radiographic knee osteoarthritis.

Exclusion Criteria:

• Age < 50 years
• History of lower extremity total joint arthroplasty
• Current cardiovascular disease or hypertension that is uncontrolled
• History of neurological disorder that effects lower extremity function (i.e., stroke, peripheral neuropathy, multiple sclerosis, Parkinson's disease)
• Current ankle or hip pain
• Currently pregnant for female participants
• Weight over 400 lbs (181.4 kg), height less than 4'8" (142 cm) or over 6'4" (193 cm), 18.5" (47 cm) hip width, or 58" (147 cm) hip circumference