I think they are mostly for riding a bike. He wore them a lot when he first started riding. Now that he is an old pro, he doesn't need them as much.
He just wore them under his jeans not alone like you would on a bike.
I'm going to force my older brother to ride with me this week when he comes visiting (he lives in Stockholm, our capital, 900 miles from here and he loves animals , so I wanna give him a real experience! :P)
I'm planning a fun trail with nice nature, bringing picnic and then of course only going as fast as he dares :P Mweheheheeh >D