The goal of this clinical trial is to compare effects of retro walking exercise versus forward walking using lower body positive pressure on knee pain, physical function, and quadriceps muscle strength in people with mild to moderate knee OA. The secondary aim is to compare effects of retro walking exercise versus forward walking using lower body positive pressure on mobility function, balance, and self-reported health outcomes in people with mild to moderate knee OA. The main questions it aims to answer are:

• Does retro walking exercise improve knee pain, physical function and Quadriceps muscle strength compared to forward walking exercise using lower body positive pressure in people with mild to moderate knee osteoarthritis?
• Does retro walking exercise improve Mobility function, balance, and self-reported health outcomes compared to forward walking exercise using lower body positive pressure in people with mild to moderate knee osteoarthritis?

Participants will walk (retro versus forward) on a lower body positive pressure treadmill.

If there is a comparison group: Researchers will compare [retro walking compares to forward walking] to see if [improve in knee pain, physical function, and quadriceps muscles strength]

Inclusion Criteria:

• Mild to moderate knee osteoarthritis
• Edge bigger or equal 40 years
• Knee pain reported by participants in the past 30 days
• One or both knees osteoarthritis graded with Kellgren & Lawrence grade 1 - 3

Exclusion Criteria:

• If they didn't meet the inclusion criteria
• History of hip, knee or ankle injury or surgery within the last year
• Kellgren & Lawrence grade > 3 of severe knee OA
• Diagnosed with rheumatoid arthritis
• History of knee injection with any medicine that reduce pain within the last year
• History of other medical condition that would disturb normal walking function
• Receive physical therapy in the last three months
• Pregnant
• Other conditions that are Contra indication to lower body positive pressure.