Chapter 4

Lecture Notes

In this slide, you can see changes in oxygen consumption during an acute bout of exercise. So while we're walking through this figure here, I want you to imagine yourself going on a run or a bike or a swim. Pick some aerobic activity and imagine yourself going through these stages. So at the very beginning in the very left part of the picture, you can see the resting levels, and the red line you can imagine to be oxygen consumption. Resting levels of your oxygen consumption, your stroke volume, your heart rate, your breathing rate, all of those things are very low at rest. And then from 0 to 5 minutes, you can see in the figure the green-shaded portion or the part labeled "Begin." This portion is called your O2 deficit, or your oxygen deficit, and here you've just started your activity, your run, your swim, your bike, whatever you decided to think about. But there's more oxygen needed by your working muscles than can be supplied until your heart rate and blood pressure catch up with this initial start of activity. And in this period, this is where you see the connection between anaerobic and aerobic exercise. So although you're participating in an aerobic exercise, some of the energy that is being delivered to your muscles to fuel those muscles to do the movement that you are producing is delivered through those anaerobic energy systems here at the very beginning, and you can see that there's this pretty sharp increase in oxygen consumption, heart rate, breathing rate, all of those things initially. And then, from 5 to about 20 minutes during your aerobic activity, you reach steady state, and here the activity becomes truly aerobic. Your breathing rate, your heart rate, your oxygen consumption, all stabilize across this period. Now imagine that you stop running at 20 minutes. This recovery period, even though you've stopped running, your oxygen consumption remains above those resting levels; it doesn't immediately drop back down to resting levels in order to replenish the oxygen supply throughout your body. And so you can see here the changes in your oxygen consumption throughout an acute bout of exercise.