In a recent article, Matt Fitzgerald claims that running low mileage, actually causes more running injuries than running high mileage. Fitzgerald suggests that running more miles will actually help you stay injury free! That’s right, Fitzgerald claims that running more miles will help prevent, not cause running injuries. In this post I’ll show why Fitzgerald’s assertion is incorrect and why running fewer miles to prevent injury can be sensible.
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According to Fitzgerald, the more you run, the less likely you will become injured. He points to a study showing runners who run only 18 miles (30k) per week are 2x more likely to be injured than runners running 37 miles (60k) per week. How could this be?
Common Sense Tradeoff
We know that sitting on the couch, running zero miles, means zero running injuries. As you get off the couch and start to run, common sense would say that your risk of injury increases. With each mile you run further from the couch the probability that you will become injured rises. The graph below illustrates this relationship.
Fitzgerald’s Backward Tradeoff
In Fitzgerald’s world, the graph would show the exact opposite. As you ran further from the couch, your rate of injury would decrease. Amazing! If I had only known this, all the injuries I’ve dealt with over the years could have disappeared, simply by running more!
Ignoring Silent Evidence
Why was it that the higher mileage runners in the study suffered less injuries? In the book, Fooled by Randomness, Nassim Taleb points out that we often ignore silent evidence.
Taleb asks us to imagine we submit a questionnaire to a group of millionaires, inquiring about their personality traits. Through the questionnaire, we find out that a common personality trait amongst all millionaires is that they are risk takers. When we find this out, we assume that to become a millionaire you need to be a risk taker. Now, suppose we submit the same questionnaire to a group of people who just went through bankruptcy. You find a common personality trait amongst them as well; they too, are risk takers. This is the silent evidence that was missing from our first questionnaire.
Now, back to the study of runners and their mileage habits. The runners completing the questionnaire had all just completed a marathon. This totally biases the results! It ignores the silent evidence of runners who ran high mileage, but never made it to the starting line, due to injuries related to their high mileage running.
Another problem with this study is the role of confounders. Did the high mileage group suffer less injuries because they ran high mileage or is there something inherent about those who run high mileage, that makes them impervious to injury? I’d argue that it’s more likely that the high mileage group has genetic characteristics that allow them to run more miles in the first place. Rather than seeing high mileage as having a protective effect, I see it as a concomitant variable associated with runners who have naturally efficient strides, and bodies more suited to long distance running. These innate traits cause a runner to run more miles, but are not necessarily caused by high mileage running.
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In my early days of running I was constantly injured. I believed that success meant running high mileage. Now I follow a low mileage approach that has helped me stay injury free. You can read more about how I run sub 3 hour marathons on 25 miles a week, or bested my 5k PR on 10 miles per week.