Not all bike riding in the pursuit of fitness has to mimic the Tour de France. Maybe a beach combing kinda day is what your body needs.
Take your trail bike out on a more level course. Even if you haven't been on a real bicycle in years, you know the saying — you don't forget how to ride. What's in it for you: sunshine, wind to cool you, and a workout with a view.
When you are weary and dreading another of the same old, same old exercise session, doing something completely different is a great way to cleanse your palate, physically and mentally. It can help you reset and return to your normal workouts with new vigour.