Over time you are most likely going to feel less pain with each workout. This is because your anaerobic threshold (AT) is getting higher. So you may be wondering what is AT? “Your AT is the heart rate you hit when you start breathing heavily, your legs start burning, everything starts to feel difficult, and fatigue sets, ” Mark Verstegen explains. As you get more fit, your AT improves allowing you to perform at a higher level for longer periods of time. Just another reason exercise gets easier by the day!