The document discusses exercise physiology and how the body's systems respond to exercise. It describes exercise physiology as the study of how the human body functions during and after physical activity. Key body systems that are involved in exercise include the muscular, cardiovascular, and respiratory systems. During exercise, the cardiovascular system works to deliver more oxygen to active muscles via increased heart rate and blood flow. The respiratory system increases breathing rate and volume to take in more oxygen. Regular exercise leads to long-term adaptations like increased heart and lung capacity and stronger, more efficient muscles.