This study investigated the effects of isometric exercises applied to the quadriceps and hamstring muscles at different knee joint angles on balance, joint position sense, and functional performance in healthy individuals. Thirty participants aged 18-26 years were randomized into four groups and performed an eight-week training program, three times per week. Outcome measures included the Y Balance Test, digital goniometer assessments for joint position sense, and functional performance tests (stair climb and 30-second sit-to-stand). The results aim to identify which knee joint angles are most effective for improving neuromuscular function and may guide future rehabilitation and training protocols.

Isometric exercises applied to the quadriceps and hamstring muscles are widely used both in rehabilitation programs and in improving physical fitness in athletes. Isometric contractions occur when the muscle generates tension without changing its length, making them especially suitable in conditions where joint movement is limited or contraindicated. Previous studies have demonstrated the benefits of isometric training in increasing muscle strength, enhancing proprioception, and supporting functional performance. However, there is no clear consensus regarding the effects of isometric exercises performed at different knee joint angles on balance, joint position sense, and functional capacity.

The aim of this study was to investigate the effects of isometric exercises applied to the quadriceps and hamstring muscles at different knee angles (15°-90°, 30°-105°, 45°-120°, 60°-135°) on balance, joint position sense, and functional performance in healthy individuals. Participants aged 20-30 years, without knee pain, previous knee surgery, or pathologies preventing ambulation, were included. All participants were randomized into four groups. Each group performed progressive resistance exercises for the hip and ankle, combined with isometric exercises of the quadriceps and hamstring muscles at the specified knee angles.

The training program lasted eight weeks, with sessions three times per week. During each session, isometric contractions were performed against resistance for 10 seconds at the assigned knee angles, with standardized rest periods between sets. The number of repetitions was progressively increased throughout the program.

Assessments were conducted at baseline and after eight weeks. The following outcome measures were used:

Balance: Y Balance Test

Joint position sense: Digital goniometer measurements

Functional performance: Stair climb test and 30-second sit-to-stand test

The hypothesis of the study was that isometric exercises performed at different knee joint angles would result in different responses in balance, joint position sense, and functional performance. The findings are expected to provide valuable insights both for improving physical fitness in healthy populations and for guiding rehabilitation protocols in clinical populations.

Inclusion Criteria:

• Age between 18 and 30 years
• Voluntary participation with signed informed consent
• No history of knee pain
• No history of knee surgery
• No musculoskeletal pathology preventing ambulation

Exclusion Criteria:

• Presence of cardiovascular or pulmonary diseases that prevent exercise
• Inflammatory or infectious pathology of the knee joint
• Uncontrolled endocrinological disorders or significant systemic/organ insufficiency
• Neurological disorders affecting knee joint innervation