A few weeks ago I wrote about negative splitting a race and the 51-49 principle (the importance of making the first half slightly slower/easier than the second half of a race). The graph on the left is a good example of what happens when you do just the opposite--positive split the course. This is from a 65-minute hill climb done as a bike test. Notice how heart rate (red) stays steady while power (black) drops steadily. The athlete simply went out too fast. This makes for a painful race or workout that is slower than it would have been had he gone out easier. Patience when racing is hard to learn. The best way to learn it is to rehearse negative splitting in workouts. What most people do in training is what you see in the second chart. This was four climbs of about 5 minutes each with a descent recovery. The intensity prescribed was just below functional threshold power (FTP). Feeling good at the start of the workout the rider exceeded FTP on the first interval. The black dashed lines show how power tailed off for each work interval. And over the course of the workout each work interval also started at too high of a power level and dropped. By the end of the workout the athlete could not get even close to FTP with interval #4. This was not a productive workout. Bad habits were ingrained and muscular endurance and force were not appropriately challenged.
The take home message here is that you race the way you train. If you want to produce the best times possible in steady state events such as running races, road time trials and triathlons then you need to pace the workouts correctly by negative splitting them. This means you hold back a bit at the start of each interval and try to gradually lift the output as the interval progresses. And you try to make the latter intervals faster or more powerful than the first few intervals. By doing this you ingrain what it takes to produce your best possible race times.
The third chart is a long ride done in preparation for Ironman Hawaii. Following a short warm up the athlete rode steadily for four hours. Notice how power (black) rises very steadily throughout and heart rate (red) remains coupled very closely to it. This chart is so beautiful it brings tears to my eyes. :) This workout was done five months prior to Ironman Hawaii in which the athlete did a 5:05 bike split. He raced the same way--steady and negative splitting the course. Learn to train this way and you will soon be racing faster.
By the way, a power meter on the bike and a GPS device for running makes this much easier to do. Trying to negatively split a workout or race based on heart rate is not always effective, especially when doing intervals.