A negative split means to run the last half of your race faster then the first half. There are multiple reasons why this is beneficial, but her is a simple explanation. Your body has only so much energy to run a race. When we perform at distances of 13.1 miles or greater, we need to conserve this energy and use it very wisely. Let’s use the analogy of currency. If you have $100 to spend to get you through the entire race, and you know that each half will cost you $50, then spending $75 for the first have will leave you with only $25 to finish. In other words, if you too much energy early on, you will deplete your glycogen stores and run out for the second half of the race. The challenge is to know your body’s limit and conserve for the first half, then spend more for the second half. Given your body’s fitness level, it would be physiologically impossible to run the first have faster then the second half and end with the same time. Meaning if you would burn out the second half and run slower. So either try to pace yourself evenly the whole race, or hold back just a bit for the second half.
When Ronaldo da Costa broke the marathon world record at Berlin in September 1998, he ran negative splits, which means he finished the second half of the race faster than the first half–a full 3 minutes faster, in fact.
Anyone can and should run negative splits however most runners don’t. Instead, they start out fast, hang on through the middle and resort to shuffling the last several miles. Those running a negative split will run a bit slower for the first third of a run, pick up the pace in the middle and finish with strength and speed.
While even 5-K racers can benefit from this negative-split technique, marathoners will find it even more beneficial.
Many people are so used to charging out and then gradually slowing down that they don’t trust their bodies will ever speed up during a run. By conserving resources during the early part of a run, they’ll be available to you at the end.
To build confidence in the method, practice negative splits during your training runs. Instead of starting your fartlek or interval sessions at the pace you want to average, run the first portion of the workout 10 to 15 seconds per mile slower. By the end of the session, you’ll be running faster than planned and will probably be feeling better than you’ve ever felt during a speed session.
Begin your race 10 to 20 seconds per mile slower than the race pace you’ve predicted. Don’t be tempted to speed up when you notice all those other runners flying by. Instead, hold back by imagining yourself comfortably passing them later in the race.
As you near the middle of the race–8 to 10 miles into a marathon, for example–you want to hit your race pace. Then, toward the end, use those fresh legs to pass as many tired runners as you can.