The rate of glycogen synthesis is directly mediated by glucose availability, and the glycogen synthase enzyme is also activated by an insulin induced signalling

The rate of glycogen synthesis is directly mediated by glucose availability, and the glycogen synthase enzyme is also activated by an insulin induced signalling cascade. Glycogen replenishment still occurs on a low carb diet, it just takes longer. If you only do crossfit every 2-3 days, and rotate the exercises you do somewhat (as is typical at most boxes) you might not notice a big difference between a low carb and higher carb diet. If you train daily and you're doing similar movements every day, you will definitely notice a difference. Since that is pretty much the modus operandi of serious athletes, that is where the whole "athletes don't do well on keto" idea comes from; it definitely doesn't apply to your garden variety recreational athlete though.