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I’m not sure exactly what you mean by climbing, but I’ll answer as a runner. I run 40-45 mpw at what I would consider a moderately advanced level. I only do a workout or long (10+ mile) run 2-3 times a week, but I do run almost every day. That being said, I do at least 19:5, sometimes 21:3, every day. I can work out any time between 8 a.m. and 1 p.m. without any problems making it to 2 or 3 p.m. to open my window and then closing between 6 and 8 p.m.
I have been doing IF for over 6 years and did not start out here, but I have been on this schedule for a few years at least. It’s totally possible to become a very efficient fat burner during exercise. You also need to train yourself to eat enough during your window to fuel your entire day and feel satiated with the right nutrients & calories. You really need to eat a lot of protein and fat, not just high volume. High volume fills you up at the moment, but dense nutrition will keep you feeling full and fuel you better.
I don’t think 16:8 is too much fasting for you to handle starting out with intense exercise, but it will take you a while to work up to more if that’s your goal.