 Hey everybody, I'm Lance Goyke. Today, we're going to discuss cardiac output. So in the previous two videos, we discussed stroke volume and we've discussed heart rate. And what cardiac output is, is it's just the combination of the two. So this is a quick one because you already watched those other two videos, correct? What happens when we start to exercise is we first beat more strongly and we increase the amount of blood that each heartbeat sends to the rest of the body. And then once that can't beat any harder or can't expand and pump more blood for each beat, once we've maximized stroke volume, then we start to beat our heart faster. And that's when we really start to feel the pounding in your chest as the heart rate increases. You can say, oh, I'm feeling tachycardia or I'm feeling my heart is racing. So the idea here is to get not only the substrate supply to the rest of the body, not only get blood to the muscles, but not only to get the energy products to, or substrates is the only word that I can think of, not only to get glucose or sugar to the muscle, but it's also to clear out all the other byproducts that are maybe keeping our muscles from continuing to work. An example might be like hydrogen ion buildup or something like that. So with cardiac output, what we're trying to do is maximize the overall efficiency of our energy delivery. Now, one special thing to talk about here is, as our cardiac output will gradually climb as we increase our exercise or as our heart rate is going up, but to a certain extent only, and it'll eventually plateau off and even come back down maybe slightly as our heart rate is really beating fast because as the time between beats decreases, there is no longer enough time to fill the chambers of the heart with as much blood. So we take away some stroke volume while increasing that heart rate. So at the very best, cardiac output starts to level off. And that's why we have ceilings. That's why we can't just keep exercise. That's why you can't just run faster to do better in your sport, right? Or you can't just keep running faster. You can't just keep running harder. You can't just try harder all the time. At a certain point, there's a physiological limit that you'll hit. And for cardiovascular exercise, that is described by cardiac output.