regular physical activity will increase the rate of diffusion from the alveoli in the lungs to the bloodstream. this keeps the body healthy as a high concentration of oxygen is being transferred into the capillaries from the alveoli in the lungs. this means that red blood cells will have a lot of oxygen to transport around the body and this allows more respiration to occur and a high production of energy. this means there is more movement in the muscles and other parts of the body because the mitochondria peform more respiration. because of this, the circulatory and respiratory system are strengthened and helps one stay in shape and be fit