The Myth of the 10 Percent Rule
Mileage increases should be based on how you respond to them, not on an arbitrary number that is often too much or too little.
Outside's long reads email newsletter features our strongest writing, most ambitious reporting, and award-winning storytelling about the outdoors. Sign up today.
Whether you’re new to running or a seasoned veteran, you’ve likely heard of the 10% rule. In short: The rule states that you should never increase your mileage more than 10% from week to week. The origin of the rule is unclear, but the genesis was injury prevention by preventing the “Terrible Toos: Too much, Too soon, Too hard.”
Regardless of the good intensions, you’ll be hard pressed to find any scientific proof for the rule’s effectiveness. It appears to be largely based in running and training lore.
Challenges and Problems
Two studies in particular have examined the validity of the 10% rule:
A 2008 study from the University of Groningen (Netherlands) included 532 subjects and split them into two groups to train for a 4-mile running race. The first group’s program was 13 weeks long and scheduled 10 percent weekly increases. The second group’s program lasted 8 weeks with 50 percent weekly increases. The first group (10% increase) had a 20.8% injury rate whereas the second group (50% increase) had a 20.3% injury rate. Despite increases 5 times larger than the rule recommends, injury rates were about the same between the two groups.
A 2012 study out of Aarhus University, in Denmark looked at 60 novice runners who tracked their running over 10 weeks via GPS. Of the 60 runners, 13 sustained an injury. The injured runners did indeed have high increases in their week-over-week mileage (over 30% increase in weekly training volume). Importantly, however, the 47 runners that didn’t sustain an injury had an average weekly training volume increase of 22.1%—double that of the 10% rule.
While it is both easy and convenient to denote a singular metric to guide volume increases, there are two primary reasons why the 10% rule should not be utilized to design a training program.
- Increases in volume are based on a pre-set, arbitrary percentage, and therefore do not take into consideration an individual’s adaptation response to training.
- The rule doesn’t scale well for different volumes. If a runner, for example, starts at a very low training volume, the initial increases would be so small that they would be deemed inconsequential. For a runner doing 5 miles per week, their weekly increase would be just .5 miles. Conversely, if a runner is at a high weekly mileage, a 10% increase would likely be too much, such as jumping from 60 to 66 to 73 miles in two weeks.
Training Stress and Adaptation
Volume increases should not be based on a singular percent, but rather based on on the ability of the individual to adapt to stress.
The goal of a runner is to stress the body followed by some form of rest, during which time the body responds and adapts to the stress, becoming better able to handle it. Repeating this process over and over is what allows for performance gains. Should a runner take insufficient rest, add too much stress, or a combination of both, their gains will likely stall or regress, ending up with them being burnt out or injured.
While it is completely normal to have days when you don’t feel great, when assessing the training adaptation response, you should see some form of forward progress over time: You can run faster/longer, you have a lower heart rate at the same pace, you recover quicker from the same workout.
It is important to note that within a training program, many weeks will stay the same or decrease in volume from the prior week. The overall progression will move upward, but the rate need not nor should not be linear, with more stress added week after week without relent.
Percent Volume Recommendations
Understanding that individual responses to increased training stress vary, here are general recommendations for maximum weekly mileage increases at different volumes.
These percentages were derived from a team of United Endurance Sports Coaching Academy (UESCA) coaches and clinicians with the focus on safe and effective programming.
The percent increases denote the maximum percent of increase and represent total weekly increase in miles. When looking at weekly increases, you should view them from a daily basis in respect to injury prevention. For example, for someone running 31 miles per week, a 15% increase is 4.65 miles. If the runner tacks on all 4 and half miles to a single run, the chance for injury is likely much greater than if the increase was distributed across a week’s worth of training, a mile or two added to each run.
Whether or not you follow the exact percentages, the two most important principles to note is that a program should not have singular percent increases and those increases should trend from high to low as the volume increases. The result is that, regardless of your mileage, you can safely add approximately one mile a week for each running day, paying close attention to your recovery, fatigue level and adaptation to higher volume.
Changes, Not Numbers
While the exact origin of the 10% rule is unknown, what is known is that it is largely myth-based and is not grounded in science. Therefore, if your goal is injury prevention, it is best to look at other areas such as the overall training load, proper amount of rest, biomechanics and strength training—than to follow an arbitrary mathematical rule.
In respect to injury prevention, the primary focus should be on increasing the training load (i.e., intensity, frequency, volume) in such a way that positive training physiological adaptations take place, but not too much load to the point that injury and/or overtraining symptoms occur. Training volume increases should be based on how you adapt to musculoskeletal stress. At no point should a singular, static percent increase dictate how a runner progresses through a training program.
Rick Prince is the founder of United Endurance Sports Coaching Academy (UESCA), a science-based endurance sports education company that offers running and triathlon coach certifications.