Runner’s second wind. How can it best described? In a word, glorious! All runners know what I’m talking about. That sweet spot that comes after about 30 minutes into your run and just when you start to feel a little tired. Then all of a sudden a burst of energy! You feel like you have wings and your breathing is better. You feel like you can run forever!
This is no mystery, however. What happens to your body is a chemical reaction. In the beginning of your run, you are burning easily accessible carbs. They are the first available energy resource which your body taps into for any kind of constant movement. They also get depleted pretty quickly, which is why you get a little tired around 20 or 30 minutes into your run. What happens then is no magic but it’s just as amazing. When oxygen reaches your fat reserves, it ignites it like fire and starts to burn fat for energy. That’s your second wind. If you are a long distance runner, you’ll experience third, fourth and many more winds as the fat storage is being torched by presence of oxygen.
Your body prefers to use fat storage for energy but fat needs oxygen to burn. Unfortunately, oxygen doesn’t reach your fat reserves until there’s constant pumping of oxygen for at least 30 minutes (can be more for some). This is why I suggest that on days you do your cardio, go for more than 30 minutes. You want to take full advantage of the fat burning stage of your cardio routine. And since our fat reserves are almost unlimited, the length of your run depends mostly on how conditioned your legs are and how much time you have at your disposal.