For more than 40 years now, one of the constants in the world of running-related injury (RRI) theories has been the “conventional wisdom” claiming that the majority of said injuries can be blamed on training errors (TE). As explained as far back as the second installment of this series [Therapy Corner #2], and reviewed/updated just a few years ago [#114], the term training errors in this context refers to a training program that involves running too much, too fast, too soon.
There have been a few numbers tossed around consistently over the years (e.g., 60% of all injuries are caused by TEs; avoid increasing weekly mileage by more than 10% per week) that attempt to quantify the problem in some manner, but the truth is these numbers have never been conclusively validated by solid research, for a couple of reasons. First, all the research (up to now) has been retrospective and correlational. In other words, the numbers were gleaned by questioning already-injured runners about their training leading up to the injury, so only an association could be made between training factors and injury, not a claim of clear cause-and-effect. Second, researchers had to completely rely on runners’ reports of their training regimen, which subjected the data to a fair amount of unreliability.
Now however, a study published in the Journal of Orthopedic and Sports Physical Therapy [J Orthop Sports Phys Ther 2018;48(10):740-748] describes an actual controlled research project that sought to determine if increasing the volume or intensity of training results in increased risk for specific injuries thought to be associated with those factors.
Prior research made speculative associations between the specific injuries of Runner’s Knee, ITB syndrome, and patellar tendinitis and increased volume, as well as tying calf muscle strains, Achilles tendinitis, and plantar fasciitis to increased intensity. But these associations were based exclusively on biomechanical models; there were no studies showing an actual relationship between these factors in actual runners, so the investigators set up an experimental study to see if this theory held.
Researchers in Denmark (The Happiest Country in the World – except for injured runners) randomly assigned runners to one of two groups. The first group increased the volume (distance) of running over a 16-week period; the second increased their intensity (speed) over the same period of time. Both parameters were closely controlled and monitored, using runners’ smartphones to track distance and speed (something that would have been very difficult to control just a couple of decades ago!), and the increased loads were purposefully greater than previous
studies indicated were probably “safe.”
The researchers were testing the specific hypothesis that those runners increasing distance would have a greater number of injuries to the knee area, while those increasing intensity would show more problems in the ankle and foot. If the hypothesis held up, it would bolster the long-held belief that training errors could be a major factor in causing injuries.
Of course, that’s not what they found. The results showed that, of those runners who developed an injury, they were pretty much evenly split in both groups – distance and speed – as far as the area of injury. Increased volume caused an almost equal number of ankle/foot injuries as knee injuries, and the same was true for the increased intensity group.
Does this mean the advice given for the past 4 decades to be cautious when increasing your training distance or speed is invalid? No – not really. It just means we can’t blame those specific factors for specific injuries. We still don’t know what the exact percentages of increased training are likely to cause problems for you; for now, the best advice it to continue to abide by the general guidelines I outlined in those previous columns and, most importantly, as always, listen to your body. If you feel unusually fatigued or sore, it’s probably a sign you need to back off a bit in your training.