First things first: don't expect to duplicate your road time in this XTERRA trail run. It is much harder to get into a rhythm on a trail because of the rocks, logs, hills, and other impediments to your swift progress. Some of the hills you will encounter on the trail will be much steeper than you're used to, and many will be strewn with rocks. There may be water to get through. Okay, you have been warned. So what can you do about it?
To start with, add some strength training, especially in the legs, to your XTERRA training. Remember, the bike ride that precedes your run is going to be more difficult than the ride in a regular triathlon. Out on the trail, you won't have the opportunity to cruise if you grow tired, and your fight with the elements will take more out of you.
Besides helping you with your conditioning and strength, stair climbing will get you into the habit of picking up your feet as you run, which is very important on a trail with rocks, roots, and stumps that can trip you.
If you have a trail nearby with hills, substitute hill work on the trail for a track workout at least once a week. In addition to building leg strength, running on the trails will help with your balance and agility, both of which will be needed on race day.
You can also add to your leg strength and endurance with stair climbing. Find a building tall enough to allow you to climb for two minutes at a moderate pace (between simple climbing and a sprint). If two minutes on the stairs is too much at first, start with one minute and build up. Once you can do two minutes, repeat six to eight times once a week. If you don't have access to a tall building, perhaps there is a stadium you can use for stair running. Go up and down five or six times once a week.
If you have access to a trail, do the same tempo runs found in the training chart in Chapter 11. The more you get used to the rough, uneven surface, the better your run will go on XTERRA race day. If you can get any information about the run course, try to find a trail for your training that has at least some of the same features. As with the riding phase, try to get to the XTERRA venue early enough to scout out the trail and run it at least once if possible.