This study aims to compare the effectiveness of eccentric and concentric quadriceps femoris strengthening exercises in patients with knee osteoarthritis. Knee osteoarthritis is a common musculoskeletal condition that causes pain, reduced joint movement, muscle weakness, and functional limitations.

Participants will be assigned to perform either eccentric or concentric unilateral open kinetic chain quadriceps exercises using isotonic loading based on a 10-repetition maximum (10-RM). The exercise program will be conducted three times per week for six weeks.

The primary objective is to evaluate differences in quadriceps muscle strength between the two exercise approaches. Secondary outcomes include changes in knee range of motion and functional capacity measured using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The results of this study are expected to provide evidence to guide exercise prescription in rehabilitation programs for patients with knee osteoarthritis.

Knee osteoarthritis (KOA) is a leading cause of pain, disability, and reduced quality of life among older adults. Quadriceps femoris muscle weakness plays a central role in disease progression and functional impairment. Strengthening exercises are recommended as a core component of conservative management; however, the comparative effects of eccentric versus concentric muscle contractions remain incompletely defined.

This interventional comparative study is conducted at the Department of Physical Medicine and Rehabilitation, Dr. Cipto Mangunkusumo National General Hospital, Jakarta. A total of 24 patients diagnosed with knee osteoarthritis based on clinical and radiological criteria are recruited and allocated into two intervention groups.

The Eccentric Exercise Group performs unilateral open kinetic chain full-arc quadriceps exercises emphasizing eccentric contraction using the NK Table. The Concentric Exercise Group performs the same exercise emphasizing concentric contraction. Exercise sessions are conducted three times weekly for six weeks. Intensity is determined using a 10-repetition maximum (10-RM) method. During weeks 1-3, participants perform 3 sets of 6 repetitions; during weeks 4-6, the protocol progresses to 3 sets of 8 repetitions.

Outcome measures include knee range of motion (measured with a goniometer), quadriceps muscle strength (assessed using the NK Table and recorded in kilograms), and functional capacity (evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]). Measurements are obtained before and after the six-week intervention.

The study protocol has received ethical approval from the Ethics Committee of the Faculty of Medicine, Universitas Indonesia - Dr. Cipto Mangunkusumo National General Hospital. All participants provide written informed consent prior to participation.

Inclusion Criteria:

• Female participants aged 40-59 years
• Diagnosed with unilateral or bilateral knee osteoarthritis based on American College of Rheumatology (ACR) criteria and Kellgren-Lawrence grade II-III
• Knee pain lasting more than 3 months with Numeric Rating Scale (NRS) score 1-3
• Limited knee flexion range of motion

Exclusion Criteria:

• History of unstable cardiovascular, respiratory, or metabolic disease
• Knee joint instability due to cruciate or collateral ligament laxity or meniscal injury
• Previous knee surgery
• History of knee intra-articular injection within the last 3 months
• Cognitive impairment (Montreal Cognitive Assessment Indonesian Version [MoCA-Ina] score < 26)
• Clinical signs of tendinopathy characterized by pain during active knee extension (open or closed kinetic chain)
• Balance disorders

This study includes only female participants to reduce variability related to sex-specific differences in muscle strength and osteoarthritis characteristics.

This study is conducted as an open-label trial. Participants and treating therapists are aware of the assigned exercise intervention (eccentric or concentric quadriceps strengthening). No blinding of participants, care providers, or outcome assessors is performed.