Episode 1: The 10% Rule Of Building Mileage
The 10% Rule sucks. This episode talks about why the 10% rule is overly simplistic (and often useless) and why mileage alone is a terrible way to judge training load.
You’ll learn how baseline fitness, workout intensity, recovery, and long runs all factor into whether your body adapts — or breaks down — during a training cycle. If you’re building mileage for a race and want a smarter way to structure your training without constantly flirting with injury, this episode is for you.
In this episode, Bryan breaks down:
Why the 10% rule sucks — and why rules of thumb fall apart without context
How baseline fitness, workout intensity, and recovery matter more than mileage alone
Why not all runs are created equal, even if they’re the same distance
Common training mistakes that lead to pain during race build-ups
Better guidelines for structuring your training so you can reach the start line — and the finish line — without constantly fighting your body
Transcript
Hey fam, I’m Dr. Bryan Kent, and this is Episode 1 of the Forward Spine & Sport Podcast.
So yes, we are doing this on the fly.
This has been a work in progress for quite a while, but we’re launching now because Boston Marathon season is well underway. Today’s topic has to do with running, the 10% rule of increasing mileage, and why, generally, it doesn’t really work.
You may be wondering: what’s the 10% rule?
The 10% rule is a general rule of thumb that’s been used in the United States for the past 50-ish years. It came out of the jogging boom, when people were like, “I’m gonna get fit,” and people were looking for ways to help prevent injury. What this rule says is that you should not increase your running mileage by more than 10% week over week.
And frankly, looking back, it might’ve been a decent idea at the time. Maybe it had some merit. But what we’ve learned is that it lacks nuance completely.
On many levels, this rule doesn’t really make sense. First of all, it basically says that if all things are created equal, then 10% should be fine. Everybody should be able to handle that. But what that assumes is that your body can handle a 10% improvement in capacity week over week, and we know physiologically that these processes take time.
When you’re just starting out and you go from running once a week to twice a week, that’s technically more than a 10% increase. Or from twice a week to five times a week — again, it lacks nuance.
What we do know is that improving your capacity for stress week over week by 10% doesn’t work in the long run. It might work for a week. It might work for two weeks. It might work for six weeks. But if you continue down that path without considering other factors, there’s a very strong chance you’re going to end up hanging out with someone like me.
Which isn’t terrible — I think I’m pretty awesome, and our team here is pretty awesome, and we’re damn good at what we do. But that’s not the point.
The point is that increasing your mileage is a very nuanced thing, and you really need to be considering other factors than just mileage when you’re thinking about entering a scheduled training plan.
Alright, so let’s get down to business.
If we’re not just considering mileage, what are we considering?
Glasses off. Serious business here.
What we really need to be talking about is load capacity, or stress capacity. What does that mean? It means how much your tissues and your system can tolerate as far as repetitive input of stress.
The tissues we need to consider are muscles, tendons, bones, ligaments, and nerves. The systems we need to consider are your cardiovascular system, your neurologic system, and your endocrine system — hormones and things like that.
Because every time you go for a run, it’s not a net positive. It’s actually a net negative during and immediately after training.
Everyone thinks, “I’m training, I’m getting faster, I’m getting stronger, I’m adapting.” Actually, it’s the opposite. You are detraining in that moment. You’re using up energy. You’re using up calories. You’re putting your systems into a state of stress, which means immediately after training, you are less able to handle more stress.
Think about it. If you’ve ever gone for a walk after a long run, it does not feel the same as it did before that long run. Walking the dog in the morning feels fine, and then you do a 20-miler and suddenly you’re dragging ass with your golden retriever pulling you down the street.
That’s because you are de-adapted in that moment. You are not fitter — you are less fit. Training has a cost, and nobody really talks about this.
If you go into training with the mindset that it’s all net positive, you can put yourself into a hazardous situation. We really need to think about capacity and tolerance.
One of the first ways to do that is by looking at your baseline — what we call general physical preparedness, or GPP.
Are you a couch-to-5K person? Or are you someone who has a long history of training? Have you been working out with a personal trainer, lifting weights, walking regularly, exposing your body to stress for a significant period of time — six months or more, consistently?
I think we can all agree that someone just getting off the couch and starting to run is less prepared than someone who’s been doing CrossFit, strength training, Barry’s, F45, OrangeTheory — whatever’s cool in your city — for six months, a year, or more.
Those two people are not the same. One has a much higher capacity to deal with stress. The other has a much lower capacity. You can’t just put them in the same bucket and say, “10% for everyone.”
That’s how people end up frustrated, asking why their friends are fine and they’re not.
Baseline matters — before you write the plan, before you sign up for the race.
The next thing we need to consider is intensity, and this is massively overlooked at every level of running.
I’ve worked with Olympic medalists and I’ve worked with couch-to-5K runners. Hot take: I really like the couch-to-5K people more. They’re a lot more fun. Everyone else is very serious.
If you’ve ever run a 5K race as hard as you possibly can, and then gone for a 5K jog at an easy, conversational pace — zone one, zone two — everyone agrees those feel very different.
But if you just track mileage, both say “three miles.”
They are not the same.
We like to think about intensity value points. An easy conversational run might be worth one point per mile. An all-out effort might be worth five points per mile.
So an easy three-mile run is worth three points. A three-mile race effort is worth fifteen points.
Your training log might say “three miles,” but physiologically those are wildly different stresses.
You might think you’re running forty miles a week, but your body might be experiencing something closer to one hundred and fifty “points” of stress.
That’s why mileage alone is a flawed system.
When I ask about training, I don’t just ask weekly mileage. I ask:
How many workouts are you doing?
How long are they?
How hard are they?
There’s a difference between base mileage and intensity workouts — hills, sprints, tempo runs, long runs. That nuance matters if your goal is to prevent injury and optimize performance.
So this whole idea of “10% and you’re good to go” is frankly useless.
If we’re not using the 10% rule as our guardrail, what should we be considering?
This is nuanced. Individualization matters. If you’re struggling or dealing with recurring pain, it’s probably time to consult a clinician or coach.
But there are some recurring patterns we see all the time in clinic.
Number one: don’t add mileage and intensity in the same week.
I know — eye rolls everywhere. People are probably ripping out their earbuds right now.
But this is almost always happening when someone comes in with a new issue.
Most training plans do this. Most coaches do this. That doesn’t mean everyone is wrong — it just means it’s highly correlated with pain and needing help.
If I’m adding miles, I’m not adding intensity. If I’m adding intensity, I’m not adding miles. If I add both, it’s brief, and then we back off.
Because it’s risky.
The next thing to pay attention to is your long run.
There was a paper recently suggesting the long run is the most important thing to monitor, and I don’t disagree. But what you want to avoid is increasing your long run every single week.
If I see a plan that goes 10, 11, 12, 14, 16, 18, 20 — that’s highly correlated with pain and injury.
Instead, consider spending multiple weeks at a given distance and building in down weeks. For example, instead of 9, 10, 11, 12, 13, you might go 9, 10, 10, down week — then 10, 11, 11, down week.
This gives your body time to adapt. Constant building without pause is a lot to ask over a long training cycle.
Another thing to consider is how many variables you’re changing in a given week. Mileage. Intensity. Number of workouts.
If you’re changing more than two things at once, take a step back.
You need weeks where your body says, “Cool. I can handle this.”
If you’re always exceeding capacity, your injury risk goes way up.
I don’t want this to be discouraging. The human body’s capacity for adaptation is nearly limitless — if you give it the right amount of time, the right tools, and the right information.
But your body has needs that outweigh the calendar goal.
You can have the best training plan in the world and the best coach in the world, but if you can’t tolerate the plan, none of it matters.
There are a lot of podcasts about pushing past your limits, and some of that is true. But we also have limits, and ignoring them can turn something joyful into something painful, expensive, and emotionally draining.
We want what’s best for you. We want you to enjoy running and movement.
So to wrap up, three takeaways:
Number one: the 10% rule kind of sucks. Any rule of thumb does, but especially this one.
Number two: you need to consider the load and the capacity of the system to tolerate that load. A little over is okay. A lot over, all the time, is not.
And number three: not all runs are created equal. You have to consider intensity.
That’s all I’ve got.
Happy running.