About 65 percent of endurance runners get injured during an average training year, and research reveals that the injury rate may be even higher in individuals training for a marathon.
Some running advocates say that 65 percent may not be so bad, because the lower-limb damage rate for sedentary individuals is probably even higher (hypothetically due to a lack of coordination and muscular strength among sofa spuds). If 80 percent of couch potatoes are hurt during an average 12-month period, running might seem rather protective.
That debate has not yet been settled. I’m doing a survey of local running clubs and non-exercising residents from the community and will let you know soon about who has the worst knees, most-painful plantar fasciae, and greatest level of discomfort in their gluteus-maximum muscles. It’s not pitfall-free research, because one can always argue that runners are pre-selected: That is, individuals who are already less-prone to injury take up running and continue running because they know that their legs will be basically OK. Meanwhile, individuals who are more-prone to injury avoid running because they know it might flare up sensitive knees. In the end, the non-runners might have lower malady rates – but not because of the strengthening effect of running.
But let’s move on and think about what can be done to lower that distressing 65 number. As we ponder this, a key thing to remember is that training is the key cause of injury in runners. Yes, it’s not shoes, a lack of flexibility, poor warm-up practices, or a too-low frequency of massage therapy. Training is the culprit.
For each runner on this planet of ours, there is a level of training beyond which injury will occur and below which workouts will proceed trouble-free. This “injury threshold” varies dramatically between runners. An elite Kenyan runner might surpass his/her staying-healthy limit with a weekly load of 25 quality miles and 100 total miles, while a novice American runner could cross over the injury threshold with just 10 total miles and one quality mile per week (a “quality mile” is one which is completed at 10-K pace or faster; for a marathon trainer a mile which is conducted at goal marathon pace can also be considered to be “quality”).
Traditionally, we have thought about the injury threshold in terms of training volume (number of miles run per week), but intensity is the often-forgotten wild card. An endurance runner who can log 40 miles per week at a moderate pace without trouble might find herself injured within a few weeks if she adjusts her training so that six to eight of those miles are quality in nature. Both intensity and volume of training have an effect on the likelihood of injury.
The good news is that the injury threshold tends to rise for each runner as strength and fitness improve. Runners should look for ways to lift the limit as high as possible, and of course they should attempt to avoid crossing over the threshold. In general, the educated runner works to keep training stresses from out-pacing adaptive processes in muscles, tendons, ligaments, cartilage, and bones.
One of the most-popular strategies for preventing injury is the use of the “10-percent rule,” which states that running volume should not increase by more than 10 percent from one week to the next. The 10-percenter has always seemed pretty reasonable to runners, since it recognizes that an injury threshold exists and that runners should be careful about moving beyond this important borderline, which has successful adaptation on the near side and injury on the far side. 10 percent would appear to be a prudent “governor” of the rate at which training volume is expanded.
But no scientific research has ever documented the benefits of the 10-percent dictum. The 10-percent rule also has a few injuries of its own. First, it focuses only on mileage, without taking training intensity (average running speed or percent VO2max or the number of quality miles) into account. Advancing volume by 10 percent from one week to the next while reducing intensity or holding it constant should place a quite-different total stress on the leg muscles and connective tissues, compared with augmenting volume by 10 percent and boosting intensity by 7 percent, for example. From an injury prevention standpoint, it is possible that intensity should be temporarily decreased whenever volume increases, although there has been little research in this area.
A second problem is that the 10-percent rule can be too conservative in many cases. For example, an athlete who runs six miles per workout, three times a week, without a hint of injury, could probably boost volume by 20 percent (from 18 to 21.6 mpw) without significantly expanding injury risk by adding in a fourth workout of 3.6 miles on another day of the week.
A third failing is that the 10-percent scheme ignores workout duration. Let’s take our athlete from the preceding paragraph. If he/she boosts volume by 10 percent, moving from 18 to 19.8 miles, he/she could run into trouble if the schedule changes to two workouts per week of 9.9 miles instead of 3 X 6.6. The nine-mile runs should have a more-damaging effect on the legs (because of the number of miles run in a state of significant fatigue), compared with the combination of 6.6-mile sessions.
Another factor that should be considered is that expanding from 20 to 22 miles per week probably is much easier to do without raising injury risk, compared with augmenting training from 70 to 77 miles per week, even though both moves involve a 10-percent change. The latter transformation would add seven miles per week – and thus more than 7000 additional impacts with the ground per week - to legs already fairly heavily stressed by training (although it could also be argued that the 70-mile per week legs would be stronger and would thus be more prepared for the advancement, compared with lower limbs which can handle “only” 20 weekly miles).
Experience suggests that a too-rapid advance in training can increase the risk of injury dramatically. However, the strategy designed to prevent overly quick advancements - the 10-percent rule - appears to be too general and unscientific to be used dependably. The rate at which a runner can increase his/her level of training is highly individualized, and it is up to each runner to recognize his/her limits. “Listening to one’s body” and reducing volume and/or intensity at the first sign of lower-limb discomfort (often with a complete rest day) is an un-scientific yet sound principle to follow. When a runner carries out a workout on sore, stressed-out legs, he/she becomes a risk-taker, not an educated trainer.
Carrying out running-specific strength training (rsst) is the most-fundamental way to lift the injury threshold. We’ll cover rsst in detail in the coming months. Educated Runner offers seminars on running-specific strength training. To sign up for one, please click on the Seminars flag at the top of this page or go to http://www.educatedrunner.com/Seminars.aspx