Adolescence is a period characterized by rapid growth and development, characterized by intense structural, functional, and neuromuscular changes in the musculoskeletal system. The rapid height growth and proportional changes that occur during this period can negatively impact athletic performance by disrupting muscle strength and flexibility. Deficiencies in lower extremity muscle strength, in particular, can lead to decreased performance and increased injury risk in sports requiring high agility, balance, and explosive power, such as tennis.

Functional training programs are holistic exercise approaches that aim to improve neuromuscular control, balance, coordination, and muscle strength by simultaneously training multiple muscle groups. This type of training is particularly important in adolescent athletes because it supports the development of strength, endurance, and explosive power. Training frequency, in turn, plays a decisive role in muscle adaptation and performance enhancement by influencing the balance between loading and recovery.

Literature contains limited studies directly examining the effects of functional training frequency on explosive power performance in young athletes. Most existing research has focused on adult or professional athletes, and experimental studies comparing the effects of different training frequencies in adolescent tennis players are insufficient.

In this context, the aim of our study was to examine the effects of a six-week functional training program implemented at different training frequencies on lower extremity explosive strength parameters in adolescent tennis athletes.

Adolescence is a dynamic period accompanied by rapid growth and development, characterized by intense structural, functional, and neuromuscular changes in the musculoskeletal system. During this period, weakness in the lower extremity muscles can lead to decreased performance and increased injury risk in sports requiring agility, balance, and explosive power, such as tennis.

Functional training programs are comprehensive exercise approaches that improve neuromuscular coordination, balance, and stabilization by simultaneously activating multiple muscle groups. These types of training are particularly important for young athletes because they support sport-specific movement patterns, increase muscle strength, and optimize the energy transfer chain. Training frequency is a key variable in determining muscle adaptation, recovery time, and load balance. Therefore, studies examining the effects of different training frequencies on explosive power development in young tennis athletes are of great scientific and practical value.

Healthy adolescent tennis players who volunteer to participate will be included in the study. After recording demographic and sport-specific information, participants' explosive strength performance will be assessed using the Countermovement Jump (CMJ), Squat Jump (SJ), Single Leg Jump (SLJ), and Reactive Strength Index (RSI) tests. Participants will be randomly assigned to two groups: the first group will participate in a 60-minute functional training program once a week, and the second group will participate in a 60-minute functional training program three times a week. The programs will last six weeks, and all sessions will be conducted by the same physiotherapist. Assessments will be conducted before and after the six-week training program. The study employed a two-group, pretest-posttest design. This study aims to demonstrate the effects of different training frequencies on explosive strength development in adolescent tennis athletes, contributing to the scientific basis of training plans for young athletes and to optimize performance.

Inclusion Criteria:

• Adolescent tennis players aged 12-18 years.
• Have at least two years of regular tennis training history.
• Regularly practice tennis at least three days a week.
• Have not had an acute injury or surgery affecting the lower extremities in the last six months.
• Have the physical ability to fully complete explosive strength tests (CMJ, SJ, SLJ, RSI).
• Individuals who voluntarily agreed to participate in the study and provided written consent from their parents.

Exclusion Criteria:

• Those with ongoing pain, instability, or deformity in the knee, hip, ankle, or spine area.
• Those who have undergone a musculoskeletal physical therapy or rehabilitation program within the last 6 months.
• Those with a systemic disease that may affect neurological, vestibular, or balance.
• Those who experience pain or fatigue to the extent that they cannot complete postural analysis or performance tests.
• Those who do not have a regular sports history or have not trained regularly in the last 3 months.
• Participants who exhibited a lack of cooperation during the assessment process that could compromise measurement consistency.