I'm switching from doing mostly road running to mostly trail running. Is there anything specific I need to know? How do the two activities compare from a fitness standpoint?

— Jim DeFarge, Bend, Oregon

Good for you. You'll find the trails a wonderful respite from the concrete and asphalt jungle. For the most part, the fitness gains on the dirt will be similar to those achieved on man-made surfaces. One fitness advantage to trail running is there's more built-in variety since hills are usually part of the packageãthis forces some interval training into your running, a huge boon to your fitness regime.

Here are a couple of suggestions regarding technique and equipment. Trails' wonderfully steep uphills are great for your leg strength, but can put quite a burden on you lungs. Use an exaggerated arm swing while you run uphill: it will help provide lift, and since your arms and legs are synchronized, you can set the tempo with your arms and your legs, willing or not, will be obliged to follow.

One of the benefits of trail running, besides being a much more joint friendly surface, is that your proprioreception, or your ability to know where your feet are without looking at them, will improve. The surface variability that you encounter on trails teaches your body to keep track of your feet, which will reduce your tendency to trip, fall or roll your ankles, and will actually make your ankles stronger. If you still have some road racing objectives, it will pay to spend a day on week on the roads in order to develop the leg speed and turnover you'll need to roll along on a hard surface.

If the trails that you are running on are very rocky or technical, you may want to invest in a trail running shoe, which will provide better protection for the balls of your feet, as well as a little protection for your toes and a touch more support.