Marianne Schwankhart's 2-Cents
For what its worth, my 2 cents below…
The best piece of advice I ever got for any training is to train in the terrain and distances you’re planning on racing. For the X-Berg Challenge, you definitely have to plan some long days into your schedule. And ideally you want to make a couple of trips to the berg to familiarise yourself with the environment. For the rest, consistency in your training and some nice uphills or step training will go a long way.
Having said that, the first year I didn’t do any training at all and managed to hang in there ok. But feeling strong brings much more joy to the occasion so I recommend training as much as one can handle before a big distance like this.