A single experimental group of adolescent athletes diagnosed with Osgood-Schlatter Disease (OSD). All participants in this cohort receive a structured, multi-week progressive rehabilitation program combined with Hold-Relax (H-R) proprioceptive neuromuscular facilitation (PNF) stretching techniques.

The intervention protocol consists of:

• Hold-Relax stretching targeting the quadriceps and hamstring muscle groups to reduce tensile stress on the tibial tuberosity.
• Progressive therapeutic exercises focusing on lower extremity strengthening, load tolerance, and functional biomechanics.

A target-specific, manual stretching technique administered by a physical therapist to address muscular tightness in the lower extremity. The protocol focuses on the bilateral quadriceps and hamstring muscle groups to reduce the cumulative tensile traction forces exerted on the tibial tuberosity.

For each target muscle group, the procedure is performed as follows:

Passive Stretch: The physical therapist moves the joint to the limit of comfortable range of motion (ROM) where mild muscle tightness is felt.

Isometric Contraction: The participant performs an active, sub-maximal isometric contraction (approximately 50% of maximum voluntary contraction) against the therapist's manual resistance for 6 to 10 seconds, ensuring no actual joint movement occurs.

Relaxation and Deeper Passive Stretch: The participant is instructed to relax completely, and the therapist immediately moves the limb passively into a newly gained, deeper range of motion, holding the stati

Knee pain during athletic activity is assessed using a 10-centimeter Visual Analog Scale (VAS). The scale is a horizontal line where 0 centimeters indicates "no pain" and 10 centimeters indicates "the worst possible pain."

The outcome is calculated as the change in the pain score (post-intervention score minus baseline score). A negative change indicates an improvement (reduction) in knee pain.

Active knee joint flexion range of motion measured in degrees of joint angle using a standard universal goniometer. The participant lies in a supine position and actively bends the knee as far as possible.

The outcome is calculated as the change in degrees from baseline to post-intervention. An increase in degrees indicates an improved range of motion.