The shoes we run in today are great for reducing impact. There are a myriad of devices, gels, air channels, etc., designed to lessen the compressive loads on the joints.
One drawback, however, is that if you do most of your running on even, paved surfaces the lower leg muscles and joints don't have to work as hard to stabilize. Joint stability and integrity are crucial for injury prevention. That's where trail running comes in.
Running over uneven and varied surfaces makes the muscles of the lower leg work especially hard; think specific strength training for the lower leg muscles. I recently noticed how sore my lower legs were after a competing in an off-road multi-sport event. The tendons, ligaments and muscles all get stronger in response to this type of stress.
Best Time Is in Base
There are a few considerations when integrating trail running into your training plan. Unless you run in off-road events, the best time to incorporate trail running into your plan is in base.
As with any new type of training stress, it's important to implement it gradually. You may want to start off with one workout per week of limited mileage, and steadily increase the duration.
Off-road surfaces vary from crushed gravel, sand, grass, single-track hiking trails, to rough back-country trails. The more varied the terrain, the more your lower legs and body will be stressed. On extremely rough and elevated terrain, hiking may be just as effective (and safer) than running. You'll likely enter your aerobic base zones in this type of terrain without having to run.
Use Trail Shoes
Trail shoes offer more support and traction, but much less cushioning. Trail shoes vary from running shoes with a more aggressive tread, all the way up to hiking shoes which may not applicable for running.
Make sure you consult with a salesperson to get the right shoe for your type of training. I don't recommend doing any road running in a trail shoe, but you can take your running shoes off road if the surface is relatively stable, such as crushed gravel.
Trail running works both the lower legs and all the muscles associated with running, including lateral knee stability, and will help develop coordination. You can continue to incorporate trail running throughout the season for strength maintenance. Trail running adds variety to your training, with better scenery!
Matt Russ (has coached and trained athletes around the country and internationally. He currently holds licenses by USAT, USATF, and is an Expert level USAC coach. Matt has coached athletes for CTS