Saturday, July 19, 2014

The 100% Rule for Running

Uh-oh…in my efforts to regain my running fitness, I think I may have made a grievous error (or narrowly avoided one, the data aren’t yet complete). Last night, my brother (who runs ultramarathons) reminded me of something I had forgotten—the 100% Rule. He said that most running experts agreed that a runner should not increase mileage by more than 100% per week.

What prompted this warning? Well, I had mentioned that I ran 20 miles in 4 consecutive days, something I have not done in quite some time. (Not 20 miles each day, mind you, but a total of 20 miles—specifically 5, 4, 4, and 7.)

Hmm, I have some questions about this 100% rule. When the percentage increase is calculated, is it always based on the prior week? It seems more useful to base it on some sort of rolling average, perhaps the average of the four most recent weeks. Suppose I ran weekly mileages of 10, 14, 10, and 2. If I based my allowable 100% increase only on the most recent week, I could only run 4 miles, far short of what I logged just two weeks ago. On the other hand, if I average these four weeks, I get a mean mileage of 36/4 = 9 miles. A 100% increase would get me to 18 miles, which seems very reasonable. Surely the experts would agree, right?

Another question: What if the prior weekly mileage (either for a given week, or for an average of several weeks) is 0? Then a 100% increase would put me at, well, 0. Even if the 100% rule were modified to something far more conservative (a 10% rule, for example), someone running 0 mileage could only increase it by … 0 miles per week.

Thus, there is a natural consequence to any rule based on a maximum percentage increase: no non-runner can ever become a runner. To become a runner, one must be born running, or must break the rule. There are no other options.

So, assuming the running experts actually want non-runners to become runners, there must be a mileage threshold below which the percentage increase rule does not apply. Rookie runners (or runners returning from injury- or dissertation-related layoffs) can dink around at the low end of the mileage continuum, until they reach the magic minimum mileage number—at that time, the 100% rule should be applied, to keep them from increasing mileage too quickly.

I wish I knew the magic number. Maybe the safest course is to assume I have already reached it,
and start limiting my mileage increases. My mileage for this week is 20 so far. Depending on whether I squeeze in another run this weekend, my next week’s mileage must not be allowed to exceed 40-48 miles.

I’m so glad I was reminded of this rule! I have really been enjoying my return to running, and I don’t want to risk ruining it by injury.