What body system is primarily affected by vigorous and prolonged exercise?

The cardiovascular system is primarily affected by vigorous and prolonged exercise because it is responsible for delivering oxygen and nutrients to the muscles and removing waste products such as carbon dioxide and lactic acid during intense physical activity. When engaging in strenuous exercise, the heart rate increases to pump more blood, thereby enhancing circulation and oxygen delivery to the working muscles. This adaptation not only increases cardiovascular efficiency but can also lead to long-term improvements in heart health, including greater stroke volume and cardiac output.

In contrast, while the musculoskeletal system, respiratory system, and nervous system are all indeed involved and affected during exercise, they do not experience the same level of direct and acute change as the cardiovascular system. The musculoskeletal system adapts through muscle strengthening and endurance improvements, the respiratory system enhances its efficiency in gas exchange, and the nervous system facilitates coordination and motor control. However, the most immediate and significant changes during prolonged vigorous exercise occur within the cardiovascular system, making it the primary focus.