If the circulatory system and respiratory system do not work together while a band member is playing an instrument, it could lead to a lack of oxygen supply to the muscles and brain. This would cause fatigue, shortness of breath, and reduced performance ability, as the body would struggle to maintain the energy needed for playing the instrument. Without proper coordination, the body may not be able to deliver enough oxygen to the muscles required for playing, leading to dizziness or even fainting in extreme cases.