Elite endurance athletes can expend 600-1000 kcal per hour during events like an Ironman.

“if you're doing an Iron Man or something like that you're probably depending on your level of Fitness um expending somewhere between 700 and 1,000 calories um kilo calor calories per hour um let's let's even be conservative and say you're really really just kind of going easy um you'd be at 600 to 700 KCAL per hour”