Feeling exhaustion after skateboarding as a total beginner?

Started skateboarding for the first time ever (M31). Learning for 3 days by now, Just now reached the point that im feel somewhat conferrable when steering and pushing, not perfect though. But when I return home I'm super exhausted and tired. I know that it is a wild comparison, But when I see competition and even general skateboarding videos, the skaters don't look tired at all. By the way I'm having a blast learning to skateboard. So far fell twice and just scratched my left elbow. At first imagined that its going to take me a while to get the flow of it with lots of injuries.