7% would not be enough for our body to actually create enough ATP molecules and to use the ATP molecules for the various processes. And that's precisely why it's the hemoglobin molecule and not the myoglobin that our body actually prefers as the carrier of oxygen, because it's the hemoglobin that can successfully unload enough oxygen. 21% in this case, and 66% in this case, to our cells of the body. Our myoglobin simply has too high of an affinity for oxygen and it will not be able to successfully unload enough oxygen to the resting tissue or to our exercising tissue. And that's exactly why it's myoglobin that is used as the storage protein that stores oxygen inside our muscle cells. But it's the hemoglobin that is used as the carrier, because it binds oxygen in a non cooperative fashion, which gives it a sigmoidal shape and it is able to successfully unload enough oxygen to the tissues of our body.