https://examine.com/nutrition/low-carbi ... endurance/
Summary
Three weeks of a LCHF ketogenic diet in elite race walkers led to marked increases in fat burning capacity during exercise, though these adaptations did not improve exercise performance, likely due to the increased oxygen cost of exercise that accompanies a greater reliance on fat. In contrast, following a HC or periodized HC diet was able to improve race outcomes and oxygen efficiency.
So even after being "fat-adapted", the Lo-Carb group's race time stayed the same after training, whereas the high carb group improved their race times significantly after the same amount of training.
I find this particularly interesting because I was under the impression different rules applied for low intensity activity and low/high-carb. Clearly this study shows differently.