[tayo42]

You have to misinterpreting something. 2.5x is 4750 calories total. Athletes are eating more then that.

[oezi]

The key insight is that you can eat more, but your body will not consume it.

https://www.science.org/doi/10.1126/sciadv.aaw0341

And nobody is saying you can't expend more energy for shorter times. It is just that you can't sustain it over long times because of our metabolic limits.