[00:01] tired but your heart never seems to? Well, when you push your leg muscles to their limit, eventually they run out of oxygen. So, they switch to a backup form of making energy called anorobic metabolism. It works, but it's far less
[00:13] efficient. It leads to changes in your muscles that ultimately cause aches and pain. Luckily, your heart works different. Its which are like tiny power plants that make energy using oxygen. combined with
[00:28] the tremendous amount of energy your heart needs to beat continuously. No fatigue, no pain. It even has its own built-in electrical pacemaker, so your brain doesn't need to tell it when to beat. Pretty neat. Over your lifetime,
[00:42] times without ever taking a break. But that same design has a weakness. Your leg muscles can cope with short periods of low oxygen. They get tired, but after a rest, they're good to go again. But your heart doesn't have that luxury. If
[00:55] it can briefly switch to anorobic metabolism, but after about 20 minutes, it runs out of fuel, and that can lead to irreversible damage. Bad [music] news. So, next time your legs are burning on a run, just be grateful they
[01:09] burning on a run, just be grateful they have the ability to recover.