Interval sessions are typically executed at a set tempo from start to finish. Whether performing shorter distance intervals (such as 400 meters) or longer, strength-based intervals (such as 1,200 or 1,600 meters), the majority of runners tend to dial in to one set pace.
In preparation for your upcoming negative split half marathon, try implementing "snowball intervals" in which you start each interval 10 to 15 seconds per mile slower than your targeted pace and finish roughly 10 seconds per mile faster.
An easily executed snowball session involves 800 meter repeats—typically five to 10 of them with two to three minutes of recovery between each. Each 200 meters should be a touch faster than the previous.
For the same 9-minute target pace we discussed in our progression run session above, they would run snowball 800's as follows:
First 200 meters: 9:10 pace (1:17.5)
Second 200 meters: 9:00 pace (1:15)
Third 200 meters: 8:50 pace (1:12.5)
Final 200 meters: 8:40 to 8:45 pace (1:10 to 1:11)
Shorter Practice Races
In preparation for any longer race, I highly recommend running a few shorter efforts for not only fitness, but also to hone any tactical skills in the last 10 to 12 weeks leading into a half marathon. You can practice how to implement your negative split properly during a shorter race such as an 8K, 10K or 15K.
In the lead up to your next half marathon, try racing a 10K in which you run the first half at five to eight seconds per mile slower than your goal pace. Then run the closing half roughly 10 to 12 seconds per mile faster than your goal pace. These efforts will give you the confidence to run more conservatively in the opening portions of a half marathon, knowing you will be able to close well.
Once you have given yourself the training tools to finish well, all that is left is race day and the reward for all your hard work.
The best execution for a negative split half marathon is to take your targeted tempo and add three to five seconds per mile. Plan to run this for five to six miles. By mile seven, move into your targeted tempo, and by mile 10, plan to be a touch quicker than your target pace.
From mile 11 all the way to the finish is where big PRs are born, and a more controlled opening can allow you to feel great during that last stretch.
According to a past issue of IAAF’s News and Notes, since spring of 2014, around 77 percent of the fastest 100 half marathon performances, both male and female, have been run in races where the second half of the race was faster than the first. And while there are exceptions to the types of races in which you should expect a negative split (mainly courses which are significantly tougher topographically in the second half), a "second half faster" approach is undoubtedly the most intelligent approach for a half marathon PR.
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