The document summarizes the different energy systems the human body uses to produce energy for physical activity. It discusses the ATP-CP, anaerobic glycolysis, and aerobic energy systems. The ATP-CP system provides energy for bursts of intense activity lasting 2-3 seconds. The anaerobic glycolysis system lasts 2-3 minutes and produces energy without oxygen through breaking down glycogen. The aerobic system provides sustained energy for longer duration activities through oxygen-dependent breakdown of carbohydrates and fats.