Assess your baseline breathing efficiency (BOLT test)

Take a small breath in and out through your nose.

Pinch your nostrils with your fingers to stop air entering your nose.

Start a timer or stopwatch.

Hold your breath until you feel the first definite desire to breathe.
This is when you may feel involuntary movements of your breathing muscles (diaphragm, neck). Do not hold beyond this point—this is not a test of willpower but of your basic physical sensitivity to O2 and CO2.

Stop the timer, release your nose and breathe in.
Your breath should be calm and steady. If you need to take a big gasp of air, or your breathing is chaotic, you held your breath for too long.

Record the number of seconds you held your breath.
This is your BOLT (“basic oxygen level test”) score.