I researched other sites' trophy guides and discovered that you can get the Exercise trophy by playing the first biking challenge over and over until you get the trophy. I can confirm that this works as I just got my plattie by doing this. This should help everyone along the way.
you can get the Exercise trophy by playing the first biking challenge.
Nowhere in the trophy description does it say you have to use the kayaking mini-game. As long as there's a jump involving 10+ coins, it will count towards this trophy, which is especially helpful since EVERYTHING in this game that involves water is very difficult to control.