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.