Triathletes who train according to the motto, "First you build endurance, then you build speed," need to be reminded that the objective of their training is to maximally adapt their physiology to swimming, cycling and running at their goal race intensity. A variety of training intensities can contribute to these adaptations, but none contributes as directly and specifically as race intensity itself.
This doesn't mean that the majority of your training should be performed at race intensity, because there's something to be said for training volume and you can do a lot more volume at lower intensities than you can at race intensity. What it does mean is that race-intensity workouts—not short intervals—should be your primary focus during the peak phase of training. This is the best way to take the general triathlon fitness you have built through the preceding phases of the training cycle and turn it into maximum race-specific fitness.
Let's look at how race-intensity training fits into the training cycle as a whole. There are two basic types of endurance training. Borrowing the terminology preferred by elite running coach Brad Hudson, we can call these two types of training aerobic support training and neuromuscular training.
Aerobic support training is low- to moderately high-intensity training in which fatigue is generally caused by fuel depletion and/or accumulated muscle damage. Neuromuscular training is moderately high- to maximum-intensity training in which fatigue is generally caused by muscular acidosis (i.e. loss of pH balance in the muscles).
For the typical well-trained triathlete, Olympic-distance race intensity falls pretty close to the threshold where aerobic-support intensity and neuromuscular intensity meet. In other words, Olympic-distance race pace corresponds to the top end of the aerobic-support range and the bottom end of the neuromuscular range.
Because the objective of Olympic-distance triathlon training is to achieve maximum physiological adaptation to Olympic-distance race intensity in swimming, cycling and running, you should do some race-intensity training throughout the training cycle. But you don't need to do too much until the final four to six weeks (the peak phase).
Doing a handful of tough workouts at or near race intensity in this phase will suffice to trigger a true race-specific fitness peak, as long as your preceding training (including a modest amount of race-intensity work) has successfully taken your general triathlon fitness to a high level.
Planning to Peak
At the beginning of the training cycle your focus should be on low-intensity aerobic-support training (long, slow distance) and maximum-intensity neuromuscular training (strength training, power intervals). As the training cycle unfolds, the average intensity of your aerobic-support training should move gradually upward toward race intensity. Your foundation and endurance workouts should get faster, tempo workouts should be introduced and so forth.
Meanwhile, the average intensity of your neuromuscular training should move gradually downward toward race intensity. Your intervals should become incrementally longer and slower.
In the peak phase, your aerobic-support and neuromuscular training should converge in a zone surrounding race intensity. (Naturally, your long-endurance workouts can be done only so fast, but the idea is to do them at a very challenging pace.)
In the final four to six weeks of training before your peak race you need not do any training at intensity levels exceeding anaerobic-threshold intensity except a few swim sprints to boost your starting ability, plus some jumps on the bike and some running strides to maintain power in these disciplines. Your key workouts in this phase should be aerobic-support and neuromuscular workouts performed at or near race intensity, and perhaps also a tune-up triathlon.
The following table provides suggested formats for these race-sharpening workouts.
2,000-3,000 steady at Ironman race pace
4-8 x 400 at threshold pace
2- to 3-hour ascending long ride: start @ Ironman pace, finish at Olympic-distance pace
30- to 60-minute time trial
70- to 90-minute ascending long run: start @ marathon pace, finish @ Olympic-distance race pace
10K run at threshold pace
1.5-to 2.5-hour steady-state ride at Ironman race pace with a 15-to 30-minute run at marathon pace
30-to 45-minute ride at threshold place with a 10- to 20-minute run @ threshold pace
The precise formats of your sharpening workouts don't matter too much. There are various workout structures that can work equally well. The formats suggested in the table above are simply my favorites.
What is important is that the pace of the workouts be close to your goal race pace for the swim, bike and run and that the workouts be very challenging without thrashing you completely.