Hey- Lately I've been biking a bit- like 15 miles every other day. I have a mountain bike and I ride on a dirt trail (the dirt is packed pretty well). It's flat the whole ride. My question: can anyone suggest any biking workouts I can do while riding on this trail. I mean- I know I could just ride further but I'm looking for some variety. I figure I could do some sprints along the way but what else is there? Thanks