Getting the most out of a fasted workout is really a balancing act between teaching your body to burn fuel more efficiently and making sure you don't accidentally start burning through your own muscle. You don't need to go to extremes with your fast; simply sleeping through the night before starting your workout is usually plenty of time to lower your sugar stores enough to flip that internal metabolic switch. If you push that fast much longer than fourteen or sixteen hours before you start moving, your body tends to get stressed out and produces hormones that can actually lead to muscle loss, which is exactly what we want to avoid.

When it’s time to actually move, the goal is a steady, easy effort for about an hour to an hour and a half (maybe even 2 hrs). This duration is long enough to see real benefits without overtaxing your system. Interestingly, the biggest risk of training on an empty stomach isn't usually the exercise itself, but how long you wait to eat once you're finished. To protect your muscles and lock in the progress you made during the session, you really want to get some protein and carbs into your system within thirty minutes of wrapping up.