To negative split is to go faster in the second half of a race leg than in the first. In reality, however, due to the layout of courses, winds and other factors, it’s more accurate to negative split your effort, applying more effort to the second half of the bike. This is a powerful strategy for three important reasons.
Start slow so you don’t blow.
Nearly everyone experiences a significant disconnect between heart rate, effort and rate of perceived exertion (RPE) in the first 20–60 minutes of the bike leg. That is, it may feel easy, like you’re not working hard at all, but your heart rate and effort applied to the bike are telling you something quite different. It can take several minutes for heart rate and RPE to reflect your effort level. By committing to backing off in the first third or half of the bike leg, you avoid the common mistakeof working too hard without realising it.
Stockpile your energy for changing conditions. Triathlon bike courses seldom get easier. Wind and heat pick up, mental and physical fatigue set in. By going easy when it’s easy, you create a mental and physical reserve to counter the increasingly difficult conditions to come in the second half of the bike leg.
Gain confidence and finish strong. These guidelines set you up for success on the run. Understand that 80 percent of the field will not be racing this way: They will ignore the early disconnect between actual effort and perceived effort, working much too hard without realising it, and not saving energy for increasingly difficult conditions. So gain confidence knowing you’ve executed the bike correctly and have set up a great run!
This advice to negative split your bike leg becomes more urgent as the length of your race increases—a long race creates more opportunities to make mistakes, and those mistakes have more time to express themselves on the run. Think you’ve ridden the first third of the Ironman bike too easy? You now have 42K to fix that. But if you rode too hard, that mistake now has 42K to express itself. How good will that bike split look wheny ou’re walking 10 miles inthe dark?
Gain confidence and finish 
