... that riding is a sport.
Doug Payne has posted a helmet cam video in which he's wearing a heart monitor, and it shows his heart working at about 88% capacity throughout. I don't know a lot about sports but I bet that's more than most people would expect. Okay, so not everyone rides cross-country courses, but still… It's too bad we don't know his weight or we could calculate the number of calories burned.
I wonder how other equestrian sports would compare?