If you’ve ever trained for endurance sports, chances are that someone has told you not to increase your training mileage by more than 10 percent per week. But have you ever wondered how the 10 percent rule came to be?
The first known person to write about the 10 percent rule in running was Dr. Joan Ullyot (1980). A medical doctor and journalist, she helped encourage people, particularly women, to start endurance running in the 1970’s and 80’s. Her advice was geared towards novice runners and followed her “rule of 10’s.” By increasing volume by only 10 percent per week, Dr. Ullyot helped reduce her running-related injuries and improve her performance. However, applying the 10 percent rule to all runners and training methodologies is not practical, nor advisable. Sports scientist Tim Gabbett advocates that the 10 percent rule “is, at best, a ‘guideline’ rather than a ‘code’ (2018).”
Differences in Calculations for Weekly Change
In a research study I conducted while completing my Ph.D. at the University of Cape Town, we tracked training in a group of 26 well-trained recreational runners for a period of six months. Figure 1A-B represents one participant and two different ways of calculating relative weekly change in training load. Figure 1A represents relative change from week to week, while Figure 1B represents the weekly relative change compared to the preceding largest week of training.
As you can see, drastically different conclusions would be drawn from Figure 1A & 1B. In figure 1A, you may conclude the runner was training randomly with huge fluctuations in weekly load. You may also conclude that on weeks when the runner increased his training, the increases were too large, with 135 percent being the largest increase. However in Figure 1B, we can interpret that when the runner had increases in training load it ranged from a 3 – 20 percent increase compared to the preceding largest week. Calculating weekly change in training load compared to the preceding largest week of training within a training program (a 20-week marathon program for example) enables us to more accurately interpret the data and can also provide runners and coaches with more practical guidelines.
Figure 1A-B. Data for Participant #4. The grey shaded region represents the 10 percent rule. A) Relative weekly change in running training stress score (rTSS) values. B) Relative weekly change in rTSS vs. the preceding largest week of rTSS values.
Most Runners Don’t Adhere to the 10 Percent Rule
The group median for maximum relative increases in load compared to the preceding largest week was 30 percent. In fact, only two participants had maximum increases of less than or equal to 10 percent and 73 percent of the participants had maximum increases of greater than 20 percent. It is important to note however, that 58 percent of participants all had a minimum of one week of decreased load between increasing weeks. The increases in load are predominantly short term (one – two weeks).
It is possible that the 10 percent guideline is too conservative for well-trained competitive recreational runners and may be a more practical guide for novice runners who are not well-trained. Well-trained runners may be able to tolerate weekly increases in training load of approximately 25 percent. However, this increase may only be maintained for a short period of time (one – two weeks).
Gabbett, T. J. (2018). Debunking the myths about training load, injury and performance: empirical evidence, hot topics and recommendations for practitioners. British Journal of Sports Medicine, bjsports-2018.
Ullyot, J. (1980). Running Free: a guide for women runners and their friends. New York, NY: Putnam.