A Just Ask Tante Pia column
By Pia Johansson
The rule says not to increase your weekly mileage by more than 10% at a time, and it might help you prevent injuries.
This rule became known as one of the golden rules of running sometime in the 80s. The rule was minted on the simple basis that runners who increased their training load too fast seemed to be more prone to injury. It is quite commonly brought up in running books and medical injury prevention practices (e.g., Can Fam Physician. 2003 Sep; 49: 1101–1109). Runners who increase their workload too fast are much more likely to suffer from Achilles Tendonitis, Plantar Fasciitis, Shin Splints, and even stress fractures! Annoying, painful, sometimes long-lasting, and common. About one-tenth of all runners allegedly deal with each of them each year.
Thus keeping in mind the 10% rule is an easy potential preventative, if you want to increase your workload (this is optional, of course). The traditional way to look at the 10% rule is to apply it to each week, but it can just as well be applied to your monthly mileage (or both). And it is also generally suggested that if you increase for three weeks in a row, then do a lower mileage week to let your body recover. Another useful application for the 10% rule is your long runs. You know, your loooong runs, the ones you don’t do every week. Increase them in about 10% increments as well. So easy. Also remember that increased workload isn’t just mileage, but also intensity (hill work included) and duration. Don’t increase all three at the same time. However, if you are a new runner, then this doesn’t apply in the beginning.
So, why? Running (and other exercise) causes low amounts of damage to your body (muscles, bones, tendons) that triggers it to not only rebuild, but to rebuild stronger: the gradual adaptation to stress. This is how you get stronger and fitter, and is part of the natural process of gradual adaptation to stress, but it doesn’t work as well if you don’t allow enough time in between workouts. Increased intensity causes more damage, and requires more time to recover and rebuild. If you don’t allow enough recovery time, you will not get the results you desire (as your body didn’t have time to improve), or, worse, you might get weaker and injured (as your body did not even have time to rebuild to pre-work out levels).
A study from 2018 looked at runners training for a half-marathon, and compared the runners training aggressively (20-60% increase in volume) versus carefully (<20% increase). They found that the aggressive training resulted in a much higher injury rate after the first three weeks, but at the end of the study there was no difference in injury rate. What this means is that your body will adapt to the higher demand either way, but you might injure yourself in the process if you do it too hard. The Association Between Changes in Weekly Running Distance and Running-Related Injury: Preparing for a Half Marathon. There are also studies that showed no difference at all (eg BMC Musculoskelet Disord. 2007; 8: 24., doi: 10.1186/1471-2474-8-24). This latter study was made on novice runners, though, where the 10PR supposedly does not apply. But, in summary, the scientific literature in favor is indeed a bit shaky. However, even though not all injuries are caused by overstraining, the doing “too much, too soon” approach is estimated to account for a baffling 60% of all running related injuries (from Can Fam Physician. 2003 Sep; 49: 1101–1109.). So whilst the scientific literature might suggest that the 10PR is too generalizing and too low (Debunking the 10% Rule), it certainly is in favor of not overtraining. It's just that how much your body can handle at this particular time of your life perhaps only you (or your body) can know. But given all of that, I still think 10% is a good place to start, and I imagine that’s what the “inventors” of the rule were thinking, too. Start slow, and then increase more if you really want, but you have to listen to your body! Personally, I think it is sometimes nice to have an easy golden rule to follow. Going from 70 km to about 80 km per month, for example, is probably quite enough for a lot of us. And if you increase with 10 kms per month for 3 months then you are hitting 100! Take it easy; don’t stress. Being a runner is not a sprint: it's a marathon.
Pia Johansson
Pia Johansson is a research scientist in neurobiology, mother of two and working mum. She was an expat for almost twenty years, in Australia and Munich and a short wild stint in Dublin many many years ago. She is in the throes of being repatriated to Sweden with her Australian husband. She likes talking, running and talking about running. And chocolate (although mostly 85% these days, as crazy as that sounds). In addition to staying fit and eating healthy, and raising happy healthy children, she dreams of doing something a little bit creative like writing or becoming a photographer. Or at least organizing her photos soon.