This group includes male adolescents aged 15-19 who have an active football license and engage in regular sports activity.

Intervention:

Name: Percussive Therapy Description: A 120-second percussive therapy protocol will be applied to each participant's hamstring muscles using a handheld massage gun (Hypervolt Go 2). The treatment includes 60 seconds on the semitendinosus and semimembranosus, and 60 seconds on the biceps femoris, performed while the participant is in a prone position.

Timing: Single session Device Used: Hypervolt Go 2 massage gun

This group includes healthy male adolescents aged 15-19 who have not engaged in regular physical activity in the past 6 months and have a BMI below 25.

Intervention:

Name: Percussive Therapy Description: The same 120-second percussive therapy protocol will be applied as in the active group, under identical conditions and using the same device.

Timing: Single session Device Used: Hypervolt Go 2 massage gun

Percussive therapy will be administered using the "Hypervolt Go 2 Black," a massage gun commonly used in clinical and athletic settings.

Participants will lie in a prone position on a treatment table. To promote hamstring muscle relaxation, a support roll will be placed under the ankle. The intervention will be delivered by the same researcher for all participants to ensure consistency. Using the round head attachment, percussive therapy will be applied longitudinally along the hamstring muscle group (from proximal to distal) for a total of 120 seconds per leg. Specifically, 60 seconds will be applied to the semitendinosus and semimembranosus, and 60 seconds to the biceps femoris. The same procedure will then be repeated on the opposite leg.

Flexibility will be assessed using the sit-and-reach test before and after percussive therapy. The best of three attempts (in centimeters) will be recorded.

Balance will be evaluated using the Y-Balance Test in three directions (anterior, posteromedial, and posterolateral). Results will be normalized based on leg length and averaged (% of leg length).

Explosive strength will be measured using the My Jump Lab app, which calculates jump height and flight time. The best result of the three trials (in centimeters) will be used.