It's been years since I've ridden real single track, but a couple of years ago I did some cold-weather riding with my mountain bike on the bridle path that runs next to a long rail-trail in this area. It was definitely more work than riding the paved path, and not just because the paved path is flatter. I would do more of it, but that bike needs some work and I don't want to spend that money right now. But it is a good workout for a relatively short ride. (Also more work afterwards -- the bike gets so dirty!)

Have I mentioned that I know someone who has already logged more than 10,000 miles in 2016? He's currently leading his home state in the National Bike Challenge. I also know the #3 person in the same state. They do spend a lot of time in the saddle.