This also lends support to "bonk training", which is an exercise fad designed to exhaust glycogen stores and then continue working out, just as a distance runner that hits the wall continues beyond to finish the marathon, or a cyclist that bonks keeps pedaling to finish the leg.
I think the point is to get your body to make the glycogen to ketone switch more smoothly, and after the bonk every calorie you burn comes directly from fat stores. For most people, exercising in ketone-mode is absolute misery, you physically can't perform at more than about 80% of what you could do with glycogen, and you can't pass your lactate threshold. So bonk trainers do that. On purpose.
I think the point is to get your body to make the glycogen to ketone switch more smoothly, and after the bonk every calorie you burn comes directly from fat stores. For most people, exercising in ketone-mode is absolute misery, you physically can't perform at more than about 80% of what you could do with glycogen, and you can't pass your lactate threshold. So bonk trainers do that. On purpose.