This study examines how sport-specific high-intensity interval training (HIIT) affects the body in elite kickboxers.

Participants are randomly assigned to either a HIIT training group or a control group. The HIIT group performs supervised sport-specific training for eight weeks, while the control group continues their usual training. Blood samples are collected before and after the training period.

The main goal of this study is to determine whether HIIT changes levels of exercise-related proteins such as apelin and irisin. These proteins may reflect how the body adapts to intense training.

The findings may help researchers and coaches better understand the effects of high-intensity training and may support the development of safer and more effective training programs for athletes.

This randomized controlled trial investigates the effects of sport-specific high-intensity interval training (HIIT) on biochemical markers related to exercise adaptation in elite kickboxers.

High-intensity interval training is widely used in combat sports because it reflects the intermittent high-intensity nature of competition. Exercise-induced proteins such as apelin and irisin are considered potential biomarkers of physiological adaptation to training. However, biochemical responses to sport-specific HIIT in elite combat athletes remain insufficiently understood.

Participants are elite male kickboxers aged 18-30 years with at least five years of training experience. Participants are randomly assigned to either an experimental group performing sport-specific HIIT or a control group continuing their regular training routines.

The HIIT program lasts eight weeks and includes supervised training sessions five days per week at an intensity of approximately 85-95 percent of maximum heart rate. The control group continues their usual technical and tactical kickboxing training without participation in the structured HIIT program.

Blood samples are collected at baseline and after completion of the eight-week intervention period. Serum concentrations of apelin and irisin are assessed as primary outcomes. Secondary outcomes include leptin, interleukin-6, and selected hematological parameters.

The purpose of this study is to evaluate biochemical adaptations to sport-specific HIIT and to identify potential biomarkers of training adaptation in elite athletes. The findings may contribute to improved athlete monitoring and the development of evidence-based training programs.

Inclusion Criteria:

• Male elite kickboxers aged 18 to 30 years
• At least five years of regular kickboxing training experience
• Active participation in kickboxing training
• Ability to complete the training program

Exclusion Criteria:

• Serious injury within the previous six months
• Presence of chronic or cardiometabolic disease
• Regular use of medications or ergogenic supplements
• Tobacco or alcohol use
• Inability to complete the training program

Individual participant data will not be shared. According to the informed consent form, personal information and study data will be kept confidential and will not be disclosed to third parties without written permission from the participants.