Sep 19, 2000

Robert DeWitt's times don't match. He thinks his marathon should be faster than it is, judging by his 10-K time.

"I have completed two marathons with times of 3:56 and 3:48," he wrote from Halifax, Nova Scotia. "Then I started doing shorter distances and completed my first 10-K in 39:10."

DeWitt called the shorter race's time "half-decent for never having done any speedwork." Then he asked, "Shouldn't my marathon time be faster considering what I've done in the 10-K?"

He's capable of a much faster marathon, I replied. One formula I've seen -- and quoted in my books -- is to multiply current 10-K by 4.7 to predict marathon time.

In DeWitt's case the math gives him 3:04 potential. This assumes he has trained equally well for the two distances, which he clearly has not since his best marathon time is 44 minutes slower.

Looked at the formula in reverse -- dividing his current marathon time by 4.7 -- he should only be able to run a 10-K in 48:30. Yet he has gone more than nine minutes faster.

This runner might be like me -- naturally better in the shorter races. My conversion factor always sat at about 5.0, meaning that a 36-minute 10-K pointed toward a three-hour marathon and vice versa.

Using this conservative 5.0 formula, DeWitt should still be able to run a 3:16 marathon. That is, if his training allows such improvement.

"Your speed is fine," I told him. "What you're lacking is the ability to exploit that speed over longer distances."

He needs more endurance training, not more speedwork, to improve his marathon. Longer long runs probably will help him the most.

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