As I have mentioned a few times now, the human body is super clever and learns when we subject it to consistent structured training... The same approach applies for when it's time to up the effort. I would have my athletes look at a 4 week period of adaption to intervals, this crosses over the end of base training, and what we are doing is preparing our mind and bodies for the change in effort.
These 4-6 weeks need to be progressive, taking the intervals from 10-15 beats above base effort up to tempo effort by the end of the 4-6 weeks. As with all intervals build them up steadily giving the body a chance to reach then recover.
While at 10-15 beats, you can keep on training most days but just drop back to base effort only the next day. Towards the end when looking at tempo, start to add a complete rest day, this again is so our body learns to recover so that once we hit the really hard sessions, our body will know it needs to recover on the rest day.
Rest and recovery becomes more and more important as we increase the intensity, this can be in the form of a day off, or an active recovery (easy spin, or swim, yoga, pilates etc.) You must remember we are only getting stronger, faster and fitter when we are resting so make sure you do.
If your focus is XC racing you can allow your training hours to drop back once intensity starts. Remember you're racing from 1.5-2hrs so a weekend recovery ride can be from 2.5-3hrs. If you're doing marathon distance, 24hr racing or stage racing then the training will be different (contact@e3coach for more details on this)
When setting your high intensity sessions it is well worth looking back at your previous seasons average racing heart rate/power/effort - this becomes your interval effort which you will work on improving. Now if you have had a good winter and spring you should find that for the same effort, you are riding faster! This is great, you need to get that ‘C’ race in and look at your performance.
Working just above your race effort for progressive intervals will help to increase your speed. Along with this, you must look at your skills. I have worked with many riders that have become stronger and fitter over winter but once we hit races, we are having too many crashes so make sure you get your skills up to speed as well. As we hit the transition from base to tempo, we must go and work on our skills... Don’t leave it for the first few races to get up to skill speed.
Do not forget your race starts!! This is so important in XC races super fast off the line, you must include starts into your intensity sessions. Getting into the first section of single track in a good place is key to the outcome of most races.
I hope this gives you a good overview of 'ramping up', as always please do ask any questions, I understand this is where it tends to get a bit more complicated in the training.