During exercise, energy demand in the muscle increases. which other body system directly provides for this demand

The body system that directly provides for this demand is the circulatory system. When you exercise, the circulatory and muscle system cooperate, in order to meet the increased needs for strength and energy. The circulatory system involves the network which delivers blood to every part of your body. This flowing of blood ensures that the tissues are oxygenated and rich in necessary nutrients. During exercise, more blood flows to and from your muscles, in order to deliver the necessary amounts of oxygen to complete the aerobic respiration.

Exercise if a form of physical activity that requires a lot of effort in order to improve one's health condition and maintain body fitness. Aside from the increase of energy demand in the muscles, the circulatory system is also affected. During an exercise, your blood flow increases due to carbon dioxide shoot up, along with the escalating oxygen demand. This causes the heart rate to speed up so that the heart can pump and distribute more oxygen and essential nutrients via the circulatory system.