Total muscle fatigue when exercising

[redpop]

Hello!

I am 2.5 weeks into keto and about 5 days into IF (16:8.) The fasting has been easy-- I basically never feel hungry on keto-- but the 3 times I have exercised since starting IF (2 pretty easy hikes, and lap swimming) I feel like I am about to keel over when I am done. My muscles feel totally and completely sapped, like I just need to lie down.
Is this normal? Did I start IF too soon? The thing is, I can stop IF but I don’t know that I would eat more or more frequently because I feel very satiated on 2 average keto meals a day.
However, before starting IF, I felt SO mentally clear and energetic. Now, my brain feels like mush and workouts feel impossible.

I need some guidance. Is this just a transition to using fat as an energy source? Or is it a sign I am doing something wrong? (BTW, I am definitely in ketosis.)

Thank you in advance.

[powertrix]

It will take your body some time to become efficient at burning the new fuel. It might be the first time in a long time that its needed to burn it in this way.

You just need to retrain your body. Although you will see performance hits in the beginning with keto, in the long term you’ll see better gains than with burning glucose.

It might take a few months to get back to where you were endurance-wise

[PaulL]

Most people take six to eight weeks to become fat-adapted, some people even longer. When you do become fat-adapted, you are likely to find endurance even better than before. Explosive performance, it has to be admitted, requires some glucose; keto fat-adaptation is not much help there.

Give your body a break and train lightly until you reach-fat adaptation. Getting your mitochondria back in the habit of using the fat-burning pathway is a lot of stress.

[redpop]

Thanks so much for your response. I’m going to stop the IF for now and go back to just keto. I’ll revisit it again later.

[PaulL]

You fill probably find yourself skipping meals and even forgetting to eat before long!