Osteoarthritis (OA) is a prevalent degenerative joint disorder that commonly affects the knee joint, leading to pain, stiffness, and functional limitations in adults. Among the muscles involved in knee function, the gastrocnemius plays a crucial role in knee flexion and ankle plantarflexion, contributing significantly to mobility and balance. Hence, the accurate measurement of gastrocnemius muscle activation is essential for understanding its role in managing OA symptoms and developing targeted rehabilitation interventions. Pressure biofeedback devices, traditionally used for muscle activation, offer a non-invasive method to measure muscle activity during specific tasks or exercises. In OA patients, the variability in muscle function due to pain, inflammation, and compensatory patterns makes using a tool that provides dependable and repeatable results crucial. However, for the pressure biofeedback tool to be a reliable measure of gastrocnemius muscle activation in symptomatic OA adults, its test-retest reliability must be established. This research aims to study the test-retest reliability of the pressure biofeedback unit in measuring gastrocnemius muscle activation while performing the isometric gastrocnemius contraction in long sitting. It is a single-group Cross-Sectional Study. Participants will be recruited based on inclusion and exclusion criteria. The participants will complete the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Scale to assess the baseline severity of their symptoms, including pain, stiffness, and functional limitations. Following this, they will perform gastrocnemius contraction in a long sitting position under the supervision of a trained physiotherapist. Baseline data on gastrocnemius muscle activation will be collected using a pressure biofeedback unit to measure changes in pressure as an indicator of muscle activation. Participants will then return 48 hours later to perform the gastrocnemius contraction in long sitting again under the same conditions, and the measurements will be repeated to evaluate the test-retest reliability of the device. Efforts will be made to maintain consistency across both sessions by providing standardized instructions and using the same equipment setup.