Participants will receive a 5-minute vibrational percussion massage (VPM) intervention applied to the right rectus femoris muscle using a handheld percussion massage device (Hypervolt, Hyperice, California, United States) with a spherical massage head at a fixed frequency of 53 Hz. The intervention will be administered by a trained physical therapist with the device applied perpendicularly to the treatment area. Two treatment locations on the rectus femoris muscle, including the midpoint and lower one-third of the muscle, will each receive 2.5 minutes of non-stroking stimulation. During the intervention, participants will lie in a supine position with both lower extremities fully relaxed and extended.

Muscle tension represents the resting tone of the rectus femoris muscle, quantified by oscillation frequency. Higher values indicate greater resting muscle tension.

Dynamic stiffness represents the resistance of the rectus femoris muscle to external deformation, with higher values indicating greater muscle stiffness and lower tissue compliance.

Muscle elasticity represents the ability of the rectus femoris muscle to restore its original shape after deformation. Lower values indicate better elasticity and lower energy dissipation.

Mechanical stress relaxation time represents the time required for the rectus femoris muscle to recover from deformation after an external mechanical impulse. Longer values indicate more compliant (softer) tissue, whereas shorter values indicate increased muscle stiffness.

Maximal isometric knee extensor strength was assessed using a handheld dynamometer. Participants performed a 6-second maximal voluntary isometric contraction of the knee extensors in a seated position, and the peak force was recorded. Three trials were performed and averaged for analysis.