International Journal of Sports Medicine

Injuries are the bane of the runner’s life. More than any other impediment, they thwart the efforts of runners to build fitness and achieve competitive goals. For this reason, injury risk management is a critical component of the training process. If there is a way to reduce injury risk, you want to know about and, if possible, implement it.

A new study in the International Journal of Sports Medicine sheds new light on how manipulating your training workload over time can help you avoid injury. A team of Dutch and German researchers enlisted 23 recreational runners to keep detailed training diaries for two years. An analysis of the data collected revealed that increases in the acute:chronic workload ratio predicted injury, where acute training load (ATL) was calculated as the average of running duration multiplied by intensity over a period of one week and chronic training load (CTL) was calculated as the average of running duration multiplied by intensity over a period of four weeks. What this study found, essentially, was that when a runner’s acute training load exceeded their chronic training load by 10 percent or more, the likelihood of an injury occurring within the next two to three weeks spiked.

The phrase “keep the ball rolling” is a summation of a training philosophy shared by a lot of today’s top running coaches that relates to the study I just described. I reflects the belief that the training process should aim toward slow, steady progress and avoid sudden leaps. Of course, a runner must first get the ball rolling in order to keep it rolling, and there’s inherent risk in this critical phase. But once you’re past it, the goal is to reduce the risk associated with workload increases as close to zero as possible without allowing progress to stall out altogether. This approach works best if you generally keep your chronic training load close to the highest sustainable level, which is to say the highest level you could keep up more or less indefinitely without burning out.

This study helped me better understand something I’ve noticed about my own running, which is that I don’t get injured as much as I used to. I’ve come to think this is largely because I keep the ball rolling. In the past, I kept repeating a cycle of getting injured, taking time off and losing fitness, getting healthy again and resuming training, going after big race goals, and getting injured again. I seldom took foolish risks in ramping up my training, but I reckon my ATL was more than 10 percent greater than my CTL more often than I realized. In any case, over time I learned what my body could and couldn’t handle, what it likes and doesn’t like, and today my personal training formula consists almost exclusively of what my body likes and can handle.

Keeping the ball rolling, for me, entails doing 14 hours per week of training in 12-12 sessions as a baseline. I repeat this routine week after week, with the majority of sessions (a lot of one-hour easy runs, uphill treadmills walks, indoor and outdoor bike rides, and elliptical rides; 30 minutes of strength training every third day) never changing. What do change are the key workouts: the higher-intensity runs and long runs. These become gradually more challenging and more race-specific as I get closer to my next targeted “peak.” The training load does increase, but very gradually, which keeps me healthier than I used to be and is okay from a fitness perspective because it’s pretty high even at baseline (except when I get COVID-19 and am out for an entire month).

Although I rely mainly on experience and tacit knowledge to keep the ball rolling in my training, there are some rigorous, quantitative online tools that runners of all experience levels can use to manage their injury risk by properly managing their training load. One is TrainingPeaks’s performance management chart, which tracks acute training load (“fatigue”) and chronic training load (“fitness”) continuously as you upload your training data. Another, which we’ve told you about in previous newsletters, is PWR Lab, an app that app analyzes smartwatch data to monitor injury risk and help runners make smart training decisions to stay healthy. PWR Lab is offering a coupon code that members of the 80/20 Endurance community.

Every runner should have a collection of mantras to use as appropriate in both training and racing. Add “Keep the ball rolling” to your collection.

There are two rationales for changing the way you run. One is to improve performance by reducing the energy cost of running at any given pace. The other is to reduce injury risk. Scientific research going back decades has consistently shown that when runners intentionally alter their natural running form, they do not become more economical. In fact, they often become less efficient. But a separate thread of research has demonstrated that certain changes in running form do reduce the risk of particular injuries.

A new study published in the International Journal of Sports Medicine is the first experiment I know of that has investigated the effects of altered running form on both efficiency and injury risk in the same group of subjects. Sixteen runners, all of them heel strikers and all suffering from patellofemoral pain (a.k.a. runner’s knee), participated. Half of them were trained to switch from heel to forefoot striking while the others served as a control group. All of the runners were subjected to tests of running economy and were asked to subjectively rate the level of pain in their knees during running. Switching from heel to forefoot striking was found to have no effect on running economy either immediately following gait retraining or after one month of practice, but it did reduce knee pain.

These findings affirm the advice I’ve been giving runners for years: Don’t change the way you run for the sake of improving your running economy and performance. It won’t work. Instead, alter your running form only if you have suffered an injury that was caused by a correctible “flaw” (scare quotes used because it’s only a flaw if it causes an injury) in your running mechanics, the heel striking-runner’s knee link being one example.

Now, every time I make this argument, at least one skeptic counters that a month (or six weeks, or however long it is) is not long enough for the energy-saving effects of a form change to manifest. Runners, they say, need more time to adapt to their new running style. There are two problems with this objection. The first is that there is simply no evidence to support it. Studies lasting as long as 12 weeks have shown that the loss of efficiency resulting from modified running form persist despite continued practice. How long is enough? Six months? A year? What is the basis for the faith that switching to a forefoot striking pattern or reducing stride length or reducing vertical oscillation will eventually pay often when it has never been found to do so?

The other problem with the common objection to my advice on running form is that running form tends to improve over time in all runners. Coaches who do teach “proper” form have told me that in their own long-term testing they have observed improvements in running economy in runners whose form they’ve modified. But what these coaches don’t realize is that these runners would have become more efficient anyway, and in fact it they probably would have improved more if their form had been left alone to evolve naturally.

This is precisely why no runner should change his or her running style for the sake of performance. The human running stride is a self-optimizing system that advances automatically toward maximum efficiency through simple repetition. You can’t make it happen any faster through conscious manipulation. Like growing a beard, you have to just let it happen.

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