Our lungs have the capacity to take in about four litres of air in each breath. In olden times, we used to take this full quota when we were active throughout the day, first as hunter-gatherers and then as crop growers. The modern lifestyle has turned us into veritable couch potatoes that barely take half a litre of air per breath. That is only one-eighth of the requirement. Our diaphragm barely moves if we are sedentary, with the result that the lower part of our lungs hardly gets any oxygen.