High-Intensity Intermittent Training and Sport-Specific Performance in Youth Amateur Boxers

Inclusion Criteria: * Youth amateur boxers regularly enrolled in a supervised boxing training program. * Age within the predefined youth/adolescent range established in the protocol. * Regular attendance to boxing training before the beginning of the intervention. * Ability to complete the standardized boxing-specific test at baseline and post-intervention. * Medical, coaching, or institutional clearance to participate in regular boxing training. * Written informed consent from a parent or legal guardian. * Written or verbal assent from the athlete, according to institutional ethics requirements. Exclusion Criteria: * Current musculoskeletal injury or pain limiting boxing training or testing. * Known cardiovascular, respiratory, neurological, or metabolic condition contraindicating high-intensity exercise. * Use of medication or substances that may substantially alter heart-rate response, unless medically authorized and documented. * Inability to complete baseline or post-intervention testing. * Participation in another structured training intervention likely to interfere with the study outcomes. * Withdrawal of parental consent or participant assent at any point.