Increasing mileage: the 10% rule?

I recently received an email from a runner who just bought my book Hansons First Marathon and was very concerned that the book didn’t follow the 10% “rule.” I know a lot of coaches, coaching handbooks, and online courses promote 10% increases in weekly mileage. It certainly sounds like a nice idea, but how does it stack up in the research department? Better yet, does it stand up in the practicality standpoint?

Luckily for us, there has been a recent interest in this very topic. In December of 2018, a meta-analysis was published in the International Journal of Sports Physical Therapy. They looked at all articles involving running-related injury as a result of training load, were randomized trials, included ages 18-65, and used runners as subjects. What’s amazing to me is that they began with a database of over 8200 research studies and by the time they were screened for eligibility, only four studies met all the criteria! What this immediately tells us is that this subject has not been looked at with thorough criteria of sound scientific principles. To me, that begs the question then, who settled on 10%? I don’t know the answer to that. It’s just one of those things where somewhere along the lines, somebody made an assessment and it’s just stuck.

So, as far as what did make the criteria, what does the data say? Unfortunately, even with the 4 studies that made the cut, there remain issues. Mainly, the lack of definition of “sudden increase” in training. From one week to the next, from day to day, a rolling average? There wasn’t continuity. However, in one of the four articles, there is some data to extract. All four studies showed that injuries increased with mileage, but failed to define the increase. In the fourth article though, three groups were looked at, 10% increases, 10-29% increases, and 30% increases. The biggest takeaway is that the 30% increases resulted in higher injury rates. The other two groups also resulted in injury rates, but there was no difference in incidence. What this tells us is really two things. The first is that there needs to be more research and clearly defined terms in this area. The second is that when considering mileage as the source of training load increase, that smaller relative increases may not have any more impact on injury rates as does moderate relative increases.

From a practical standpoint, I feel like there a few factors to consider when deciding how much to increase your mileage. The first is where you are currently are with your running. Believe it or not, with a lower mileage runner, we can probably be a little more aggressive, in terms of percentage increase. Let’s take a look at a couple of examples.

 

10 Miles/week 10% Increase 20% Increase 25% Increases
Week 1 11 12 12.5
Week 2 12.1 14.4 15.63
Week 3 13.31 17.28 18.75
Week 4 14.64 20.74 22.5
Week 5 16.1 24.88 28.13
Week 6 17.71 29.85 35.16
Week 7 19.48 35.83 43.95
Week 8 21.44 43 55

 

By looking at the chart above, you see that we are using a starting point of 10 miles per week as the starting baseline. In this example, we are using this for a new runner and only looking at running volume. I am excluding other training variables, like intensity, for now. If you start at 10 miles per week and increase your mileage by 10% per week, it would take you two months to build to 20 miles per week. On the flipside, if you believe what research is indicating, and increase by 20% per week, we can knock that time in half. I’ll discuss this more in a second, but let’s discuss the 25% column. You can see at week four, we are almost the same as 20% and just over 20 miles per week. However, after that, you really start increasing the mileage. To double your mileage in 4 weeks is one thing (when starting low), but to the more than double that number again in the next 4 weeks is another issue. To me, when starting at a low number like 10 miles per week, the sweet spot for increasing weekly volume is 20-25% to get to a weekly mileage in the 20-25 miles/week range.

But why do I need to increase that fast?

Won’t I get hurt? Why am I referencing for 4 weeks? Why are 20-25 miles important?

These are all questions that I found myself asking while writing this, and I assume you are asking something similar. So, part of the answers to these involves the research, while the other involves my observations from coaching. Four weeks appears to be a good amount of time to build just your mileage before adding some other source of training load increase. We can do that in four weeks and not significantly increase the risk of developing a running-related injury. I can get a runner to focus on just adding mileage while keeping the intensity low, not take forever to do it, then allow them to get into a training program. I like the 20-25 miles per week because it opens a lot of doors to whatever it is you want to do. Once you get to 20-25 miles per week, you can maintain that, start adding intensity and run a pretty solid 5k within the next 6-8 weeks. If you are marathon training, it allows us to add “slower intensity” and longer run while scaling back the rate at which we increase the volume of training. We are still gaining fitness, but we are adjusting the variables at which we increase.

Now, everything we have talked about so far was to get a runner from initial lower mileage to a solid base level to then start structured training. So, the initial focus was simply more mileage at easier paces, then allowing to shift away from adding mileage as fast but insert more intensity. Once we get to a level of about 30 miles, I don’t think you can continue to add mileage at that 25%. It’s almost a reverse scale. The below chart shows where I think you can be confident in increasing mileage and where I would use caution and where I don’t think it’s a good idea at all.

 

10% 15% 20% 25% 30%
30 miles 3 Miles 4.5 Miles 6 Miles 7.5 Miles 9 Miles
40 miles 4 Miles 6 Miles 8 Miles 10 Miles 12 Miles
50 miles 5 Miles 7.5 Miles 10 Miles 12.5 Miles 15 Miles
60 miles 6 miles 9 Miles 12 Miles 15 Miles 18 Miles

 

Think about it this way. At lower mileage, you have a lot more room. You may be able to add another day for a couple of the increases. Then start increasing your long run on the weekend, then a mile to a weekday run, etc. Eventually, you’ll get to a point where you simply can’t just add another day or more mileage to your runs. You’ll also be at a point where you are doing structured workouts and so you’ll be increasing your training load based on that, too. So, by increasing your mileage while doing workouts means you’ll be adding volume, frequency, and intensity. Increase all three by too much at the same time and that is where the body begins to break down.

To summarize, when starting at a low weekly volume, take 4-6 weeks and add volume through easy running at a rate of 15-25% per week. Then back the rate of increasing volume to allow for the addition of intensity, along with gradual increases in daily volume and frequency of runs.

Up until now, all the discussion has been centered around the first time getting to a weekly volume. However, what if you are coming off from planned downtime (post-race)? Or, what if you were training at a lower volume, say for a shorter race, but want to get back up to a higher volume for a marathon segment? Overall, the general theory is the same for my athletes. As long as the volume is something you were able to tolerate previously, then you can certainly be much more aggressive than 10% per week increase.

My general rule of thumb is that the first week of running is about 50% of the desired weekly mileage.

So if you want to be at a peak of 50 miles per week:

  1. Then I’d run 25 miles that first week.
  2. The second week could see an increase of 25%, to 31.25 miles.
  3. The third week could be a 20% increase, to 37.5 miles per week.
  4. Then the 4th week could a 10% increase to 41.25miles. At this point, you are about 80% of the peak mileage and healthy place to start introducing workouts.

That’s a summary for what I do post-marathon, but if you are coming off a shorter race like a 5k or 10k, you can probably get away with a 2-3 week buildup and then start workouts during the 3rd or 4th week back. Granted, this is all dependent on the fact that you are healthy or the source of the problem has been addressed.

To me, the biggest takeaways are that there’s not a lot of research to show that 10% should be a hard and fast rule when increasing your mileage. Like a lot of items in training, it’s dependent on your factors. It’s also more about a relative percentage that makes the most sense. A 30% increase at 10 miles per week is a lot more reasonable than a 30% increase at 50 miles per week. Lastly, I feel like we have had much more success when focusing on mileage first at low intensities before slowing the rate of volume increase to accommodate more intensity. Granted, if you know you are injury prone, maybe focus on become more resilient before trying to make big jumps, or explore common themes when you became injured- it may not be the mileage at all. Experiment with what you can tolerate, but don’t think you have to be suck in the 10% rule. 10-29% appears to be the same in risk for developing running related injuries. Keep that in mind the next time you are designing your plan.

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