High-Intensity Interval Training Effects on Fitness in Youth Soccer Players

This experimental study was designed to examine the effects of an 8-week HIIT protocol, applied three days per week, on selected physical performance parameters in youth soccer players. Participants were randomly divided into an experimental group and a control group. Height was measured using a Harpenden stadiometer and body weight using a digital scale. Aerobic performance was assessed using the Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IRT1), with heart rate monitored via a Polar Team Pro 2 device. Anaerobic performance was evaluated using the Running-based Anaerobic Sprint Test (RAST). Blood lactate concentration was measured using a portable lactate analyzer from finger-tip capillary blood samples at rest and following the RAST protocol. All measurements were taken as pre-test and post-test assessments, before and after the 8-week intervention period. The study was approved by the local Clinical Research Ethics Committee (2021/243) and conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from the parents/legal guardians of all participants prior to testing.

Inclusion criteria

• Active male soccer player registered in the U19 category at Sivasspor A.Ş. Football Club
• Regularly participating in team training sessions prior to the study
• Voluntary participation with written informed consent obtained from parents or legal guardians
• Free from any injury or health condition preventing participation in high-intensity exercise

Exclusion criteria

• Presence of a musculoskeletal injury within the past 3 months
• Diagnosis of any cardiovascular, metabolic, or chronic health condition
• Attendance rate below 90% during the 8-week training program
• Withdrawal of consent by participant or parent/legal guardian