The Power Meter Handbook: A User’s Guide for Cyclists and Triathletes

average power was 245 watts. That means your VI was 1.04 (256 ÷ 245 = 1.04). Is that good or bad? My general rule of thumb is that for steady-state races your VI should be 1.05 or less. A VI of 1.0 would mean perfect pacing: NP was the same as average power. There were few spikes, and they were small. A VI in excess of 1.05 tells me that you probably wasted a lot of energy by surging and generally not riding steadily.
    A while back I received an e-mail from a triathlete who had finished an Ironman the previous weekend. He was disheartened, for even though he had a good bike split time, he had to walk the marathon. “What went wrong?” he asked me. Fortunately, he was using a power meter, so I could look at his race graph. His VI was 1.21. That’s what I would expect to see in a 1-hour, hilly criterium. It was much too high for an Ironman bike leg. He was surging frequently throughout the race, wasting energy, and creating lots of acidosis—big-time fatigue! No wonder he walked the marathon.
    Variability Index has little relevance to the analysis of nonsteady, variably paced races, such as road races, criteriums, and mountain bike events. By their very nature, they are highly variable. You can’t ride steadily without spikes and surges and still be a contender in these races.If you have a low VI, you are just a finisher—or you had a great team protecting you.

    Figures 5.3 and 5.4 provide examples of high and low VI from races. In the road race example of Figure 5.4 , it’s easy to see from all of the power spikes why VI is so high. In contrast, note how small the spikes are and how steadily the Ironman triathlete rode as shown in Figure 5.3 .
Steadily Paced Races
    When I coach triathletes and time trialists, I devote a great deal of training time to teaching them how to properly pace. Pacing is difficult to master, but it is much easier to do with a power meter than with a heart rate monitor or through the use of perceived exertion. In fact, with power it’s almost like cheating. Whereas most athletes in such steady-state events start the racemuch too fast, the athlete with a power meter can monitor output, which is much more closely related to performance than is input (see Chapter 1 for a discussion of output and input in racing). All it takes is deciding in advance the power range that you are capable of using during the race to produce the best time. This is determined largely by tracking past experience, by using Intensity Factor, and by knowing your duration-based Peak Power levels from your Power Profile, as described earlier. If it’s a 40-km time trial or triathlon and you know it will take you about 1 hour, then you also know that your P60 is about the power you should be aiming for throughout the race. But there’s a bit more to it than that since courses typically have small, rolling hills that take a few seconds to go over or even severe climbs lasting several minutes.

    A triathlete once asked me what he should do on the downhill portions of an Ironman bike course. Should he pedal hard, pedal easy, or coast? That was a great question and one that gets at the heart of proper pacing on a bike. It has to do with drag—how much wind resistance you encounter as the bike goes faster or slower.
    On a bike, as your speed increases linearly (a straight line from, let’s say, 20 to 25 mph), the power required to go faster increases exponentially. This is owing primarily to aerodynamic drag from air resistance. So while going from 20 to 25 mph is only a 25 percent increase in speed, there is something like a doubling of the energy required to achieve that additional 5 mph. As speed increases, you must use more energy to sustain that speed, plus additional energy to overcome an increased headwind.
    Why am I telling you this? Because as you go downhill and your speed increases, should you want to go even faster than coasting allows, the energy “expense” of the additional miles per hour is going to cost you dearly. If you try to go really fast by pedaling hard downhill, you’re going to dip verydeeply into your precious carbohydrate stores while causing an increase of hydrogen ions and resulting acidity in your blood. Doing that repeatedly will soon catch up with you. You’ll eventually be forced to slow down as a result of wasted energy and acid-bathed muscles. A wasted race.
    The bottom line for pacing has to do with an old adage that says that if you are riding on a fast portion of a course