Broadly speaking, training off-road adds many qualities to your overall fitness and technical abilities. Mountain biking gives you power, strength and endurance. And by powering up short, sharp hills and over obstacles, it’s adding an extra level to your fitness and strength endurance.
You can simulate this by doing a mix of power intervals 10-30secs long and some longer threshold intervals of 2-10mins up a climb. I recommend devoting about 50% of your weekly training time to cycling. In most Xterra races, the bike leg will be over half of your total race. To build aerobic fitness, you should be doing at least one long, steady aerobic ride each week/every 10 days.
With practice, your body learns to recover quickly and to push over the climbs and technical sections. This is important in mountain biking as you need to keep the momentum high, and is great practice for hilly, technical road courses.
Off-road training gives you added skills on the bike, such as keeping a high cadence. It will also help with technical road triathlons by giving you the confidence and skill to take corners fast and ride cobble sections smoothly. Your upper body strength will be improved, too – a lot of mountain biking is how you handle the bike through technical terrain, not how the bike handles you.
It’s a similar situation with off-road running: you learn to look at what’s ahead as you’re constantly changing pace, which is good for road triathlons that may have corners, laps or steep up and down hills. It’s also great to have the change of pace to pull away from your competitors. Again, off-road running develops your upper body strength – you need to work your arms just as much as your legs as you power up the steep hills.
Most importantly, off-road training is fun. It takes your mind off having to deal with traffic and crossing roads. I guarantee that a 90min off-road run is far easier on your legs than 90mins pounding the pavement. You will also recover quicker. Also, since doing Xterra, I’ve mentally overcome many challenges, such as punctures, mechanicals, unrideable sections and even a few crashes here and there. All of this helps you become a stronger athlete.
There are no secrets to training off-road: you have to do what’s right for you and to your own limit. Enjoy being at one with nature and relax. Don’t focus too much on numbers; the ever changing environment will naturally improve your all-round fitness and technical abilities thus improving your overall race confidence.