Know the terrain...

Unlike alpine skiing, mountain biking is all about well-defined paths and trails. One needs to faithfully follow the doted line (single track for that matter) and try to remember its incline, its ridding surface and its idiosyncrasies.

Not knowing or not remembering these particularities will cost a lot in terms of strain, suffering and mental frustration. Not knowing or remembering doesn't allow for conserving momentum at the end of a downhill to carry to the steep section.

It also puts too much burden on the brain, which already processes a lot of information by staying concentrated and watching like a hawk and has little desire to deal with extra uncertainty, anxiety or fear when the rider is spooked by some unexpected surprise. I've always thought that mental strain is the worst of all, because it has enough power to literally “cutting one's legs.”

So, in summary, when you venture on mountain bike trails that are reasonably difficult and that you've never visited before, expect to expend an extra 80% energy (I didn't measure, it just came to me as the right number!) so if you are comfortable riding 15 miles of single trails you know, never go for the same distance on some itinerary you've never experienced before; settle for just 8 miles, that will be more than enough!