Rethinking the 10 Percent Rule for Increasing Mileage

By: Matt Frazier

For the past five weeks, I’ve experimented with a training schedule that’s entirely new to me, with great success. It’s simple:

1.  Run every day.
2. Start with just 20 minutes each day.
3. Each week, increase the length of the daily run by 10 minutes.
4. Do less when you need to, but not more.

(So far I’ve used Rule #4 only twice, running for half an hour on days when I should have run 50 and 60 minutes. It was largely due to time constraints, but I think that rest did me well.)

Why these rules?

This certainly isn’t the most efficient way to train — for that, you’d want long runs, rest days, and varied workouts.

Instead, I’m doing this as a way to get reacquainted with running, after a two-month layoff following the Rock n Roll USA marathon. I thought of all the things that had kept me from running consistently over the past few years, applied some rules of habit change, and this was the outcome.

To say the new plan has worked is an understatement. My enthusiasm for running has been completely renewed; I’m devouring running books, dreaming big about races, and for the first time in my life, genuinely looking forward to my run each day — for its own sake, not just for its role in a training program.

This has partly to do with the way I’m running, but that’s a story for another post.

But what about the 10 percent rule?

In terms of the 10 percent rule that runners are so fond of reciting — “Never increase your mileage by more than 10 percent each week” — my plan that has worked so well appears completely backwards.

The jump in the second week, from 20 minutes each day to 30, represents a 50% increase in mileage. Then, to 40 minutes, it’s a 33% increase. Even tomorrow, when I jump from 60 to 70 minutes per day, it’ll be a 17% increase.

What’s more, the 10 percent rule will fail on the back end, too. At some point my increase of the run length by 10 minutes each week will become unsustainable. I have no way of knowing when that will be, but I’m guessing it’ll come in another month as I approach two hours of running each day — precisely when the amount of each jump dips below 10 percent!

There are two lessons here.

First, the 10 percent rule doesn’t apply when you’re running below your baseline.

Your baseline, as running coach Jason Fitzgerald puts it, is the mileage level where you’re comfortable but not struggling. Even if you haven’t been training recently, you can estimate it based on your history and what mileage has met that criteria in the past.

Until you reach your baseline, you can increase mileage more aggressively, as I have. I’m approaching mine now, but because the intensity of my runs is very low as I’m focusing on rebuilding the aerobic base before taking on harder workouts, I’ve still got some room.

If you’re a beginning runner and don’t yet have an established baseline, the 10 percent rule still isn’t of much use at the outset. Check out Jason’s post railing against the 10 percent rule for more about why.

The second lesson is that the 10 percent rule doesn’t apply when you’re at the upper end of what you can handle.

For example, let’s say I get up to 85 miles per week with this new plan, exceeding my previous peak by 20 miles or so. I’d be thrilled to get there and I think it’s possible. But at that point, a 10 percent weekly increase will mean close to 9 miles.

In other words, just a month after hitting the extremely high level (for me) of 85 miles, I could “safely” get to over 120 miles per week if I naively followed the 10 percent rule each week.

As optimistic as I like to be, that just ain’t going to happen.

(This isn’t to say my 10-minute plan will be any better than the 10 percent rule at that point. I designed it to help me get started again; if I get to 70 or 80 miles I’ll need to adjust the plan and start spending more time at each level.)

Ending the tyranny of 10 percent

I’m not saying we should throw out the 10 percent rule entirely. For most of the running we do, in a mileage range that’s moderately challenging, it’s not a bad rule of thumb.

But most people pay attention to the rule at the beginning of their training, perhaps when they’re returning to running after a layoff like I am. And that’s the wrong time to abide by it.

Listen to your body as you increase the mileage up your baseline, and then follow the 10 percent rule from there. Once you near the upper edge of what’s comfortable, it’s back to listening to your body for the signals that you need more time or that it’s okay to proceed.

And speaking of listening, that’s been the focus of my workouts during these past five weeks of the most enjoyable, relaxed running of my life. More on all of that in an upcoming post.

Have a great week of running!