Blood Oxygen Level Test. This is a good quick indicator of how sensitive you are to CO2 and can help you in endurance or better breathing habits. Breathe in, breathe out so there’s no air in your lungs and hold your breath. You are now forcing your body to use the oxygen it has stored in your blood. Healthy adults should be getting over 30 seconds and aiming for 1 minute. It’s a very rough way of seeing how much of your blood oxygen you can use before your oxygen hunger becomes too much. By repeating this test several times in a row daily, it’s a really quick, easy method of making your body work more efficiently without straining yourself!