The aim of this study is to measure and compare the femoral cartilage deformation after walking on the treadmill and tartan floor in patients with knee osteoarthritis (OA) and healthy volunteers.

The investigators will recruit 30 patients who will be applied to Physical Medicine and Rehabilitation outpatient clinic and diagnosed with knee OA according to American College of Rheumatology (ACR) criteria and 30 healthy volunteers matched for age and gender. The sociodemographic characteristics and detailed history of the patients included in the study will be questioned and recorded. After a detailed physical examination of all patients, weight and height will be measured, and body mass indexes (BMI) will be calculated. Participants' physical activity levels will be determined based on the World Health Organization's Global Physical Activity Questionnaire. This questionnaire has been reported to provide a valid and reliable estimate of physical activity, Turkish validity and reliability have been established.

A repeated measures design will be used in which healthy volunteers and patients with knee OA all complete all loading conditions (30min walking on the treadmill and tartan floor). For this, each group (healthy volunteers and knee OA patients) will first walk on the treadmill and then do tartan ground walking 1 week later. Femoral articular cartilage thickness before and immediately after walking will be measured with portable ultrasonography (USG) with a telemedicine feature.

Upon arrival at the treatment unit or area of the tartan track, participants will sit on a treatment table with their knees fully extended for 30 minutes to minimize the effects of previous activity on cartilage. All sessions will be completed at the same time of day to reduce daily variations in cartilage thickness. The dominant leg will be defined as the self-reported limb that the participant chooses to use to kick a ball. All post-load USG procedures will be achieved within 5 minutes after the loading condition. 3 images will be taken from each participant.

Two separate evaluators will measure to determine the reliability among the measurers.

To equalize the loading, the speed at which each participant walks on the treadmill in 30 minutes will be determined by the pedometer as a brisk walking speed (5 km/h). Again, each participant will walk on the tartan floor with a pedometer and walk for 30 minutes at an equal distance at the same pace as on the treadmill. The pedometer will give a warning when it is below or above the desired speed.

Inclusion Criteria:

• Be over 40 years old
• Having been diagnosed with knee OA according to the ACR diagnostic criteria
• Being diagnosed with stage 1-2 knee OA according to the Kellgren-Lawrence staging criteria

Exclusion Criteria:

• Having a musculoskeletal or systemic disease that will prevent the exercise
• History or symptoms of lower extremity surgery, ligament injury, balance disorder, lower extremity injury in the last 6 months
• Presence of psychiatric or neurological disease affecting cooperation, cognitive and neurological functions