Hmm, I would say could be a combination of several things, technique, gear set-up, and condition for sure. As soon as you ride “relaxed” you don’t cramp up so much which results in much better muscle performance. Thus less burn. I am not saying ride relaxed by not giving all you have, but by mastering a perfect technique. The better the technique the more relaxed you will ride.
If your gear set-up is “off” in terms of what “your” body structure requires you can’t ride relaxed.
And if you are out of (boarding) shape you need some more days of riding to get your muscles used to it.
My opinion
Ray