Boxing is an intermittent combat sport that requires repeated high-intensity actions, sustained punching output, and rapid post-exercise recovery. This single-arm field-based study will examine the effects of a nine-session high-intensity intermittent training program on sport-specific punching output, heart-rate responses, and accelerometer-derived movement responses in youth amateur boxers. Participants will complete a standardized boxing-specific test before and after the intervention. The primary outcome will be the total number of punches completed during the test. Secondary outcomes will include round-by-round punching output, heart rate immediately after the test, heart rate one minute after the test, one-minute heart-rate recovery, and the accelerometer-derived sum of absolute acceleration peaks recorded during each round. The study is designed to provide ecologically valid evidence on feasible monitoring strategies for training adaptation in amateur boxing.

This study is a field-based, single-arm pre-post intervention conducted in youth amateur boxers. The intervention consists of nine sessions of high-intensity intermittent training integrated into the athletes' regular boxing preparation. The training approach is designed to reflect the intermittent physiological and technical demands of boxing, emphasizing repeated high-intensity efforts, incomplete recovery, and sport-specific execution under fatigue.

Before and after the intervention, participants will perform a standardized boxing-specific test composed of repeated 30-second punching rounds separated by recovery periods. Punching output will be recorded as the number of completed punches per round and as the total number of punches across the test. Heart rate will be measured immediately after the test and again one minute after completion to characterize acute cardiovascular response and early recovery. In addition, smartphone accelerometry using Phyphox will be used as an exploratory secondary monitoring strategy. Accelerometer data will be processed using the absolute acceleration signal, and local acceleration peaks will be identified within each active round using a predefined operational criterion.

The primary purpose of the study is to evaluate whether a short high-intensity intermittent boxing-specific training block is associated with changes in sport-specific punching output. Secondary objectives are to describe changes in post-test heart-rate response, one-minute heart-rate recovery, and accelerometer-derived indicators of movement intensity. Given the applied training context and the expected small sample, the study will be interpreted as exploratory and field-based rather than as a definitive efficacy trial.

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.

Individual participant data will not be shared because the study involves minors and a small sport-specific sample, which may increase the risk of indirect identification. Results will be reported only in aggregate form. Non-identifiable summary data or analytic procedures may be made available upon reasonable request, subject to institutional ethics approval and participant confidentiality safeguards.

Masking is not feasible because participants and coaches are aware of the exercise training intervention. Outcome processing will follow predefined operational criteria to reduce analytical discretion.