I wore these when learning to snowboard and although they are not heavy duty in terms of protection, they cushion the falls so I wasn't covered in bruises. It definitely improved my learning experience, as a few friends were struggling to sit down comfortably by mid week but I was fine. They basically feel like you are wearing snug lycra shorts with lumpy padding on. The waistband is snug too. I'm a size 14 and the size 42 were fine but snug. They need to be failry snug so that the shorts dont move too much during the activity. They fitted easily under my slightly baggy snowboard trousers abd no one could tell I was wearing them.
I'm a size 10 and the 38 fitted well. As said not serious impact shorts (my partner does the park stuff on snowboard and he wears 3d ones which solidify on impact) but for beginner snowboarder not doing anything too wild these are great for cushioning falls. Still hurts when you fall hard but these really take the edge off, so glad I got them.