Great article from TrainingPeaks on how to accomplish a 100 mile mountain bike race.
or many endurance athletes, a 100-mile mountain bike race is either a bucket list event or the capstone of their season. This distance takes both mental and physical training to properly prepare. The appropriate balance of endurance training and specific race preparation is important to ensure success.
You’ll want to start at least 28 weeks out from your race so as to have plenty of time to effectively integrate the three key periods of training. Using the base, build, and specialty phases will allow you to gradually build your endurance, threshold, and anaerobic capacity so that you’ve prepared all of your body’s systems for the event.
The Base Phase
The start of your race preparation will be the base training phase. Depending on your current level of fitness, this period should last approximately 12 weeks. During the base period the focus should be on building a strong aerobic base. Having solid endurance to build upon is critical for a successful 100-mile race. It’s during the base period that you’ll want to perform longer sub-threshold efforts to push your aerobic capacity.
This is also a good time to integrate strength workouts into your training to help prevent injury as you begin to gradually increase your volume and intensity. Remember that this is not the time to do hard anaerobic efforts- that time will come. Think of the base period as the foundation on which your successful season is being built. A couple of key workouts during your base period are:
Sweet Spot Intervals
20 minute warm up in zones 1 and 2. Then perform 30 to 45 minutes in your sweet spot (90 to 95 percent of threshold). Finish the ride in zone 2.
20 minute warm up in zones 1 and 2. Then perform 30 to 45 minutes at the top end of your zone 2 range. Finish the remainder of the ride at endurance pace.