Is the 10% Rule Still Valid?
A. The 10% Rule
One of the biggest questions many will have as a new runner once they get started is to know just how much they can safely progress their training load to allow themselves to develop fitness while preventing injuries along the way. As one begins to scour the internet looking for guidance on the topic, there’s a strong chance that they will come across what is known as the “10% Rule”.
The 10% Rule appears to have been most likely coined by Dr. Joan Ullyot in 1980. Dr. Ullyot, a journalist and medical doctor, proposed that (novice) runners should not increase their weekly running volume by more than 10% per week to help prevent running-related injuries. This rule has become status quo that most athletes and coaches use for guiding training progression throughout any individual training block. Some of the instinctual counterarguments that arise will go something like this: “So if I only run 10 miles per week, are you saying I can only increase my mileage by 1 mile per week?” Of course not. The reality is that this rule, like many, is highly generalized and may be appropriate for a certain runner with a certain training background that is looking for a conservative, easy to follow progression plan. I think there is probably a sweet spot where the 10% rule works, for the low-moderate mileage runner, running between 20-40 miles per week. Less than that, the weekly gains may be too minimal, more than that, the weekly gains may become too aggressive for some. The biggest flaw in this rule is that is approaches training from the perspective that running volume is the only parameter to modify in training progressions. For example, I may keep a runner at 30 miles for two consecutive weeks, but maybe I progress them from all easy runs in one week to now a week with one workout and one true long run. This is where I think, “Don’t change two things at once” is a better rule to follow, and is a more holistic approach to managing the stressors that the athlete is enduring on a week-to-week basis.
B. What is the Actual Guiding Principle?
Going back to lesson 101, the answer is of course – it depends. Just how aggressively one should progress their training depends on just how active they were prior to beginning training and if they did any running beforehand, just how much. For most non-runners beginning running for the first time, I will usually start them out with about 3 days of run/walk intervals beginning with a total of 10 minutes of running, and progress them to running alone once they are able to run 20 minutes continuously. How long it takes them to progress to 20 minutes continuously will depend on their overall level of fitness and just how well they are adapting to training. And that last point is really the key to all of this: the runner themselves dictates how fast or slow to progress through a training plan.
Based on the athlete’s physical fitness level and with the subjective feedback I receive from them, I will then focus on progressing each individual training session, which naturally results in the volume for the week progressing likewise. But rarely do I ever actually calculate the % increase in mileage from week to week. This highlights, I believe, the value for new athletes in finding a good coach to help them to distinguish between normal fatigue and aches/pains vs. burnout and injuries creeping in. The mantra that I hold close and repeat constantly to myself is from Renato Canova, “The runner shouldn’t follow the training plan, the training plan should follow the runner”. The training plan is written, but it’s written on paper with pencil, and is always subjective to change daily depending on the subjective wellbeing of the athlete.
C. The 10% Rule – Still Valid, but Different?..
There was a recent 2025 study that was making the rounds on the internet that proposed that the 10% Rule is still valid, but in a different way than we have perceived it to be up until this point. The study was completed by researchers out of Denmark and what it found was that in the 1820 injured runners out of the 5,205 that were recruited, the vast majority (72%) of the injuries that were accrued were considered to be overuse and developed suddenly (during a single training session) rather than gradually. Because of this, the researchers essentially claimed that the 10% Rule should still be followed, but that it likely refers to increasing volume within a single training session rather than over the course of a week. In other words, what athletes should really be worried about is increasing their running volume by more than 10% within a single session. While increased running volume itself is of course a factor in training related injuries, there are a few problems I have with the conclusion:
1. The study only collected mileage data from the participants within a 30-day period and linked self-reported injury complaints from the participants to the changes in running volume alone. There was no analysis of the intensity or type of runs that the participants were doing. This is a big area of questioning for me because I would argue that a 30-mile week with 2-3 hard workouts for example would carry much higher injury risk than a 45-mile week of easy running.
2. Injuries that develop during a single individual training session may more so highlight strength deficits or be due to specific training errors than an increase in running volume. I would use two examples to support this anecdotally. Twice before when I strained my soleus because I began running up an extended uphill section of road shortly after jumping out of the car, putting excessive eccentric strain on the muscle before it was warmed up, this was an obvious, single session injury that developed due to a unique training error that occurred fairly early in the run. In the summer of 2025 when I strained my proximal hamstring on my 19th 400m interval during a track session, that was a training induced injury because of a prolonged, intense workout that relied heavily on glute activation. The total volume in the workout was not any greater than what I had been accustomed to in the past from a pure mileage standpoint, and admittedly, I was not doing regular strength work that might have helped prepare my body and prevent the injury from occurring in the first place.
3. They highlight that even a small increase in training load of anywhere from 1-10% will increase injury risk by up to 19%, indicating that even a 10% increase in mileage may be too aggressive. This would mean that anytime a new runner is attempting to increase mileage by one mile at a time (i.e. 3 to 4 miles or 4 to 5 miles) on weekly training runs, they would always be in violation of this 10% rule up until they reach at least 11 miles for a single run (11/10 = 1.09 = 9% increase in single run mileage). So, to avoid violating this 10% rule, new athletes would need to make sure they never increase their longest mileage run to date by more than ¼ mile or ½ mile at a time until they get to at least 11 miles. Unless I am coaching somebody that simply wants to run and stay healthy at all costs with little to no care about performance (which does happen sometimes), I think this approach is a little too conservative and brings me to my final take home point below.
4. Runners get injured. This unfortunately is part of sport, no matter how much technology and medical knowledge we try to throw behind our athletes. As coaches and medical providers, we should deal with this by trying to analyze ever possible factor at play leading to those injuries when they come up instead of making decisions based off of broad generalizations.
D. Injuries as Part of the Sport
It’ s probably universal that anybody that has been running longer than a day has experienced an injury, whether it be minor or major. Anytime you are trying to up the ante and develop fitness in training, there is always a potential for injury, and their cause is going to be multifactorial. What I always tell my athletes is that injuries are likely inevitable, and what’s important is that we are equipped and prepared to deal with them when they come up. The key points I would hone in on are not any set rules, but on these points:
- Increase training load gradually by listening to your body
- Swap in impromptu cross training or rest days as needed
- Stay consistent with strength training, especially when the athlete has a history of recurrent injuries.
- Focus on consistent good workouts over any single great ones. The margin gains that can be obtained on any single day pale in comparison to the potential losses if sidelined for several weeks or months.
References:
Bettin, Allison. “A New Approach to the 10 Percent Rule.” TrainingPeaks, 5 Aug. 2020, www.trainingpeaks.com/blog/a-new-approach-to-the-10-percent-rule/.
- “Nyt Studie Af Løbeskader Omskriver Historien: Din Skade Kan Komme Efter Kun Én Løbetur.” DR, 10 July 2025, www.dr.dk/nyheder/indland/nyt-studie-af-loebeskader-omskriver-historien-din-skade-kan-komme-efter-kun-en. Accessed 14 Apr. 2026.
Schuster, Jesper, et al. “A Paradigm Shift in Understanding Overuse Running-Related Injuries: Findings from the Garmin-RUNSAFE Study Point to a Sudden Not Gradual Onset.” JOSPT Open., 1 Oct. 2024, pp. 1–18, https://doi.org/10.2519/josptopen.2024.0075. Accessed 13 Apr. 2025.
—. “How Much Running Is Too Much? Identifying High-Risk Running Sessions in a 5200-Person Cohort Study.” British Journal of Sports Medicine, 7 July 2025, p. bjsports-109380, https://doi.org/10.1136/bjsports-2024-109380.