The aim of this study was to evaluate the energy requirements of the aerobic oxidative, anaerobic lactic (glycolytic), or anaerobic alactic systems in highly trained amateur boxers during a 3×3-min-round boxing fight. On three separate occasions, 10 highly trained male amateur boxers undertook a progressive treadmill run, a progressive bag-punching exercise, and a full-contact competitive boxing fight of the 3×3-min format. Expired gas and heart rate (HR) were recorded throughout all exercise tasks, with the exception of a gas analysis during the competitive fight. Total energy expenditure and the contribution of the three major energy-supply systems were calculated based on oxygen uptake (V̇O<inf>2</inf>) and HR during exercise, blood lactate accumulation, and excess V̇O<inf>2</inf> during the fast phase of the recovery. The blood lactate concentration was >15 (range: 12-18) mmol·L-1 after the fight. The HR reached >93% of the maximal (HR<inf>max</inf>) in rounds 1 and 2 and >97% in the final round and was strongly correlated with HR<inf>max</inf> (r=0.885). The average calculated O<inf>2</inf> uptake during the boxing fight was 89% of V̇O<inf>2max</inf>, whereas O<inf>2</inf> uptake equivalent calculated from the involvement of all three major energy supply systems was 122% of V̇O<inf>2max</inf>. The calculated energy provision during the fight was 73% aerobic, 19% anaerobic alactic and 8% anaerobic glycolytic. In highly trained male amateur boxers, 3×3-min boxing match elicits very high HR and blood lactate levels with predominant involvement of aerobic and substantial contribution of anaerobic alactic energy systems.