The 10% myth

This article was originally posted by Ryan at the original Blogs.

Everywhere you go, you hear about it. Even those of us who try to avoid hearing about it can’t get away from it. The "10% rule". That supposed rule that a person shouldn’t increase their weekly mileage by more than 10% from week to week or they will risk injury, fatigue, burnout, and a multitude of other bad repercussions. Of course, a corollary to this rule that some strongly promote is that, as long as you are within this guideline, you’re perfectly safe. Is this really true? Well, let’s look at a few facts as well as some observations I’ve made.

First, let’s look at the numbers. We’re told that this "10% rule" applies to everyone at all levels. OK, so how does a person start running? You can’t increase from zero miles by 10% and end up with anything but zero. Maybe that’s why so many people are afraid to start running. They would be breaking the "10% rule". OK, that’s a little extreme so let’s take a situation I was once introduced to. Someone ran 8 miles in a recent week and was asking what would be reasonable for the following week. This person mentioned that, by Wednesday, she was already on the verge of breaking the "10% rule" but still felt good, so did she really have to stick with 10% or could she go higher? I gave my usual advice, listen to your body and let it guide you. After all, is it really reasonable to expect a person to go from 8 miles to 8.8 to 9.6 to 10.5? If she was to do 9 or 10 miles that first week after the 8 mile week, would that mean sure injury or burnout? What if she tried to stick to 8.8 miles but measured a course wrong and ended up running 8.9 or 9 miles? She broke the 10% rule, now she’s going to get injured? Let’s be realistic here. There was no doubt in my mind that she was ready for 10, 12, maybe even more miles. Maybe she would have to maintain for a short time once she hit 12 miles but everything she said suggested that she was ready. Of course, that didn’t stop a "10% rule" proponent from saying I’m full of it and that she should in fact run 8.8 miles the following week, 9.6 the week after, and 10.5 on the third week. This person informed me that it was a proven and time tested principle. Really? I’d love to see the evidence of that but I’ll get to that later.

What about the opposite end of the spectrum? Some of those who promote this "rule" say that, as long as one stays within the guidelines, they will be fine. What does this mean for someone who just ran a 100 mile week? Well, that person runs 110 miles the following week, 121 the week after, 133 the next week, 146 on the fourth week, and 160 on week five. That’s a 60 mile per week increase in barely over a month. Staying well within these boundaries, a person could increase by 6 miles per day in a month’s period. What are the chances that someone could actually increase the training load this quickly without problems? Again, let’s be realistic here.

Next, let’s look at some facts. A number of sources will tell you that, as long as you increase by 10% or less, you are at a low risk of injury and burnout. As soon as you cross over to more than 10%, though, you are at a high risk of injury and burnout. This is a very interesting theory. All I can do is ask what makes 10% so special? I know of many people who, on a very regular basis, increase their mileage at a much higher rate with no repercussions. I have actually done that myself from the beginning of my running years. I also know of many people who have increased by much less than 10% and ended up with very serious injuries. From my observations, I have seen no sign that 10% is some magical turning point where injury risk suddenly increases. Also, I have seen no studies that have found this to be the case.

In the end, I just have to ask why 10%? Simple, it’s a nice round number that sounds good. It’s a middle ground. Many people get injured increasing at 5% or less per week, many others don’t get injured when increasing by 20% or more per week for a short period of time. Most runners will be safe at 10%, although many would also be safe at 15% and those who wouldn’t be safe may or may not be safe at 5%.

Well, if most runners are safe at 10%, why do I have a problem with this number? Simple, there is a better, less limiting and even safer way to increase. It’s called listening to your body. At points, if you listen to your body, you will probably increase your mileage by more than 10% per week. This is the point where 10% is too conservative and is actually limiting your training. At other points, if you listen to your body, you will probably increase your mileage by less than 10% per week and maybe even stop increasing for a few weeks before starting the buildup again. This is the point where 10% is too aggressive and runners who follow it to the letter end up developing problems.

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