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Many of you have probably heard of ‘the 10% rule’ – the notion that one should increase mileage by a maximum of 10% per week in order to minimize your risk of injury. In practice however, this rule is fairly arbitrary and doesn’t make sense in many situations. We’re going to look through some of those situations and discuss more appropriate ways in which you can plan how you increase your mileage.

The 10% rule is often misinterpreted as meaning that 10% is an ideal level of mileage increase, rather than emphasizing 10% as a limit as to what’s a ‘safe’ amount to increase by.  In addition to this, it’s generally not clear whether the rule should be applied for a number of consecutive weeks or whether it is simply a once-off increase.  This leads to problematic situations where a runner may believe that they should be increasing their mileage by 10% every week which will very quickly lead to a huge amount of mileage as the increments compound.

Even if we apply it as a once-off ‘limit’, the 10% makes very little sense when we are working at the extremes. For a beginner runner, moving from 10kms to 11kms is certainly a very reasonable increase and it wouldn’t be unreasonable to have an even bigger increase. At the other end of things, for an elite runner to jump from 100kms to 110kms is a fairly significant amount in comparison.

As we’ve spoken about on many previous posts; the concept of using mileage as an indicator of training load has many flaws in itself. By equating an increase in mileage to an increase in training load, we’re assuming that all other factors within a week are staying the same.  In reality, every week will be different and a higher mileage week with a lower amount of intensity could produce a far lower stress on our body compared to a week with a lot more intensity. This means that we really shouldn’t be comparing mileage from week to week with too much precision; or without at least taking these other factors into account. On top of this, some runners may have a mix of trail and road running in their training which will have a different level of impact on their body. In other words, not all mileage is created equal.

So, with all this in mind, how do we go about increasing our mileage in a safe and sensible manner?

Firstly, let’s introduce a concept called ‘baseline mileage’.  This is a figure that represents how much mileage you can do fairly comfortably on a weekly basis.  This provides a much better benchmark for your level of mileage rather than simply looking at the past week or two, as it provides a meaningful long-term figure of what sort of mileage your body is adapted to.  When looking at increasing your mileage, we’d use this figure as the amount that we are increasing from; rather than simply looking at an increase from week-to-week. 

As an example, let’s take a runner with a baseline mileage of 80km per week. Let’s say that this runner has done the following mileage over the past few weeks: 50km, 65km, 85km. At first glance, it may look like they’ve had some pretty drastic jumps in their level of mileage. But once we take their baseline mileage into account, we see that the big increases are in fact very reasonable, as they’re operating well below their comfortable level of mileage and then making only a small increase above their baseline mileage. 

Personally, my favourite way to increase mileage is in a block-styled approach rather than trying to increase it for a few consecutive weeks. This would involve an increase in mileage followed by a ‘stabilizing’ period; where you maintain that mileage for a few weeks until it becomes comfortable and then repeat this process. When instead taking the approach of increasing mileage for a few consecutive weeks, it can be hard to maintain your training quality while dealing with this constantly increasing level of stimulus. This is particularly applicable for more experienced/advanced runners who may already have a fairly high level of mileage and are likely to take a bit longer to adapt to a change in stimulus.

There are certain instances where one can be a bit more aggressive in how they progress their mileage, and other cases where you need to exercise a lot more caution. When coming back from a rest period or from some minor injury/sickness, it’s usually safe to ramp your mileage back up to normal levels pretty quickly. For instance, a runner doing 100km a week might start with a 50km and build back up to 100km over a 2-3 week period. Conversely, any time you are going into ‘unchartered’ territory and doing more mileage than ever before, it’s best to exercise a lot of caution and increase very slowly and gradually.

With all this being said, it’s important to remember that mileage should seldom be something that is detrimental to the quality of your training. For short periods of time, it’s ok if an increase in mileage requires a lower intensity of training. But in the long-term, you should be aiming for a level of mileage that enables you to feel good for your workouts and allows you to maintain the quality in your training.  Mileage is something that only really makes a difference when it compounds over periods of weeks and months; so, whenever you’re unsure, rather take the slightly more conservative approach that you know will enable you to train consistently – rather than taking risks to squeeze in a few extra few miles just to hit a particular milestone. 

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