Our body and cells get oxygen from the air we breath in. Unfortunately, the air we breath in consists of about 20% oxygen and 79% nitrogen. As there are not any multiple choice answers, one would logically assume that he would need to increase his oxygen intake. So on logic alone he would need to breath more or deeper longer breaths that allow for more intake.
I cannot imagine anyone running a 5K would carry around a portable oxygen tank, however, this would allow for extra oxygen intake as an oxygen tank is straight oxygen and as I stated before...when we breath the air from around us it only contains about 20% oxygen.
There is also Cellular respiration now that I think about it. Perhaps by the intake of food and the effective breathing would allow for him to increase his oxygen intake. When you exhale your lungs release the carbon-dioxide that is produced from the oxygen in your blood that breaks down sugars.
Reference to wiki-pedia: Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. (I am unsure how to add photos, so you will need to see it on the site.)
Best of luck to you on this one. I am a medical student at college level, however, this refers to a man running a 5K. If it were a patient they would be placed on oxygen first and foremost as the main and effective way of increasing there oxygen intake and set with a schedule for food. Hopefully some of this could be of use to you.