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Why Aren’t Run Calculators Always Accurate?

BY Hal Higdon

Run pacing calculators are fun toys and can help us estimate performance, but they are not perfect.

Have a question about running? You’re in the right place. Every Tuesday, world-renowned coach, author and athlete Hal Higdon posts and answers athlete questions here. You can submit your question by joining the discussions on Hal Higdon’s Virtual Training Bulletin Boards.


Using your training programs, I have completed many half marathons with my last three averaging under two hours: 1:54. I’ve run two full marathons using your Intermediate 2 program both times. But my full marathon time is way off from my predicted times. I should be around 4:15-4:30 for the full according to predictors, but I’ve yet to break 5 hours. I run only one full marathon a year. My third full is coming up, and I don’t feel much faster than last year. Why do you think my time for the full is so much slower than predicted, and what can I do to match my potential?


With a sub-two half I would expect you should be able to run even faster than the times you quote above: maybe close to a sub-four for the full. And you seem to have put in the training. One possibility is that although you say you have run “many” half marathons, you only have done two fulls. That’s not a lot of data to work with. The course? The weather? Perhaps you even overtrained? A lot of problems can arise to thwart our ambitions. It took me five years before I finally ran a marathon that matched my times at shorter race distances.

But another possibility is, maybe you are more sprinter than marathoner. More fast-twitch than slow-twitch muscles. Most people land in the middle in the talent pool; others have success at 100 meters or 26.2 miles, but not always both events. Think of Usain Bolt, the world record holder in the 100 meters at 9.58. In a long-distance race, you would sprint right by him well before the so-called Wall. Match any of the fast Kenyans who run so well in the marathon in a 100 against Bolt, and he would be into his bow-and-arrow pose before they crossed the finish line.

Predictors are fun toys and can help us estimate performance, but they are not perfect. It’s unclear to me what might be holding you back. All I can say is, keep on trying.

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About Hal Higdon

Hal Higdon is a Contributing Editor for ‘Runner’s World‘ and author of 34 books, including the best-selling ‘Marathon: The Ultimate Training Guide’. He ran eight times in the Olympic Trials and won four world masters championships. Higdon estimates that over a quarter of a million runners have finished marathons using his training programs, and he also offers additional interactive programs at all distances through TrainingPeaks. Hal uses TrainingPeaks to power his interactive marathon and half marathon training plans — check out more of Hal Higdon’s training plans on his website.