Get access to everything we publish when you sign up for Outside+.
It’s well-known that runners suffer a lot of injuries; by many accounts, about half of all runners will be sidelined at some point each year. Less known is what exactly causes this huge rate of casualties in a non-contact sport. A new study suggests we may even know less than we think we do.
The standard answers point to basic risk factors such as high volume, high intensity, or running more than five or six days a week. But are these really the sources of our woes?
To find out, a team led by Jean-Francois Esculier of The Running Clinic (headquartered near Montreal, Canada) and a medical professor at the University of British Columbia pored over 36 studies featuring a total of 23,000 runners, looking for trends.
The findings, published September 3 in the Journal of Athletic Training, began by confirming that injury rates are indeed high. Of the 23,000 runners, 26 percent got injured in the course of training programs that were generally a lot shorter than a year, indicating that the per-year injury rate is quite probably close to the 50 percent commonly cited. They also found that competitive runners are injured more often than novice or recreational runners.
Beyond that, however, conventional wisdom came up lacking. All the standard risk factors appear to be oversimplified. In general, Esculier says, it’s not possible to say that exceeding any given level of volume, frequency, or intensity of training increases your risk.
Nor do easily measured changes in training, such as rapid increases in volume or intensity seem to be the culprit.
“[That] surprised me a bit,” Esculier says, “because clinically, mostly, when they tell me about their injury, they say they changed something. I was expecting to find some sort of link in the literature.”
Part of what’s needed, he thinks, is a more sophisticated way of measuring the stress factors that might lead to injury.
For example, he says, the studies on injury causation don’t measure cumulative intensity (or changes in it). It’s possible that mileage, intensity, and rest are indeed risk factors, but that it’s the combination of them that matters, and the interconnections are too complex for standard research protocols to spot.
Furthermore, stress is stress, regardless of its origin. “If you don’t consider recovery and sleep and nutrition and hormonal cycles, you’re missing the point,” he says.
Stress levels from other aspects of life can also play a role. “If you have a new love, you might tolerate a 30 percent increase in volume with no problem,” he says. But even a dramatic cut in workload might not be enough “if you’re sleeping half of what you used to because you just had a baby.”
The oft-cited rule that increasing weekly volume by no more than 10 percent a week is safe is also problematic. To begin with, Esculier says, a 10 percent per week increase for a beginner doing 10 miles per week is “an entirely different thing” than for someone doing 150 miles per week. Not to mention that increasing by 10 percent a week doubles your mileage about every 7 weeks. Do that for a year, and the 10 mile-per-week beginner hits 1,400 miles a week. The 10 percent rule begs the question: for how long? And then what? Some elites report increasing their standard base mileage by 10 percent a year, not a week.
Injury By Any Other Name
Another issue is the definition of “injury.” The scientific literature isn’t all that consistent on this, but the most commonly used definition is one developed by Tiê Parma Yamato, at the University of Sydney, Australia. In 2015, she polled 38 researchers around the world and came up with the following definition: a running injury is pain that causes a “restriction” of training for a week, or a stoppage for three consecutive training sessions.
It’s a definition that casts a very broad net, one that encircles a lot of runners who are quite fine, thank you. As a coach, for example, I teach my runners the “Rick Lovett cure-all for all niggles: three days off.” It’s not unique to me, it’s one of the “secrets” followed by many of the ’70 and ‘80s road running greats (who are still running), including Bill Rodgers and Amby Burfoot.
Three days doesn’t necessarily cure you, but it’s the first step in nipping incipient injuries in the bud. But by Yamato’s definition, the moment people do this, they’re already classified as injured. If every precautionary cutback in training is ruled to be an injury, no wonder the scientific literature can’t figure out what’s going on.
Your Mileage May Vary
Not that Esculier thinks injuries don’t have causes. But instead of looking for the type of broad, numbers-based rules of thumb runners often hear, he says, it appears that “recommendations probably need to be individualized.”
Esculier wasn’t the only one surprised by the findings.
“I thought it would be clear cut,” says Bob Williams, a long-time coach in Eugene, Oregon. “[Something like] mileage, change of surface, not enough recovery, too much jump in mileage.”
Like Esculier, however, he agrees that the new findings don’t prove that injuries don’t have causes. Rather, they appear to show that the variables that produce them are too complex and runner-specific for the studies to catch.
My own experience supports that. In my running and coaching, I’ve found that major culprits can be incredibly runner-specific, such as a sudden shift to running on slanted surfaces, running too much downhill (that one that did me in more than once) or pushing through after asking myself at the end of a workout that’s not going well, how much damage can it do to finish it? (If you ever find yourself asking that, there’s only one answer: a lot.)
“It’s more of an art than finding [the perfect] numbers,” Esculier says.
So what really causes injuries?
As Esculier’s study found, the answer isn’t as simplistic as we once thought it was. There aren’t any magic numbers below whose thresholds you will be consistently safe, and above which your injury risk mounts.
But it remains likely that a leading cause of injury is changing “something.” Or, more precisely, changing it too rapidly.
Which means the answer comes down to the oldest canard of all: listen to your body. If you pay attention to your overall stress level, and make small, incremental changes at whatever rate your body tolerates, Esculier says, “I think you will adapt.”
It’s actually a remarkably old-school concept.
Williams ran for the University of Oregon in the 1960s, coached by the legendary Bill Bowerman. “[He] never emphasized mileage,” Williams says. “He emphasized real recovery between tough sessions.”
And when something did go wrong, his view was also highly individualized. Forget all the weekly tallies and other magic numbers in your training log. “Let’s look at what you’ve been doing in the past ten days,” William’s remembers Bowerman would say. And that would inevitably reveal what was causing the problem.