Might be a lack of potassium or magnesium? For me if I have muscle soreness, it’s one of these
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For OMAD (keto), I have to fairly liberally season some of my food with salt and potassium (no salt) to keep up or I’ll start feeling sore like you mentioned. If I keep up, typically no issues. The trick is finding which foods to season because man… no salt is NOT my favorite flavour