Probably sit-ups, planks, and back extensions.
If you’re really on top of your game, you might be picturing side leg lifts, the glute bridge, and other hip strength exercises, because you know that hip weakness been connected with a litany of running injuries. But a provocative new paper published last year proposed that there’s another core you need to worry about—the “foot core.”
Is Your Foot the Key to Running Injury Free?
Patrick McKeon and collaborators from four American universities laid out their theory in a paper in the British Journal of Sports Medicine.1
In the article, the authors draw parallels between the core muscles of the abdomen and spine and the small muscles within your foot itself.
The authors state that although these “plantar intrinsic” foot muscles are very small and not very strong, their role isn’t to create motion. Instead, they stabilize the foot, providing a solid foundation for the larger, more powerful muscles in the lower leg to efficiently move the foot.
The biomechanics of the foot are a little unusual, because it has to alternate between stiff rigidity and springy flexibility during walking and especially during running.
The human body has developed a number of mechanisms that allow for this, and McKeon et al. argue that the small plantar intrinsic muscles inside the foot are one of them.
Another biomechanical quirk of the foot is that the major muscles which control your foot motion, and even your toe motion, aren’t located in the foot itself. The main muscles that scrunch up your toes, point your ankle down, or roll your foot outward are all in your lower leg, adjacent to your calf muscles.
These so-called extrinsic foot muscles are already popular targets for strengthening in rehab programs—think towel scrunches, theraband ankle exercises, and so on. But, as McKeon et al. point out, these exercise don’t do as much to stimulate the plantar intrinsic foot muscles.
Fatigue in Foot Muscles and Injury Risk
The centerpiece of McKeon et al.’s hypothesis is that proper functioning of the “foot core” is essential to being able to walk and run without injury. With scientific research focusing mostly on hip dysfunction as a cause of injury in the past decade, the paper’s authors worry that researchers are missing an important piece of the puzzle.
There is some evidence that foot muscle function plays a role in biomechanics:
A 2008 study by researchers at the University of Virginia showed that doing an exercise that fatigued the foot muscles causes the arch to collapse slightly,2and another study of eight people with plantar fasciitis in one foot found smaller and presumably plantar intrinsic muscles in the injured foot than in the healthy foot—though this could also just be the result of favoring the healthy leg.3
Since the idea of a foot core is very new, McKeon et al.’s discussion of the practical implications of this idea is rather brief.
In addition to calling for more research, the authors recommend the use of a special maneuver called the “short foot exercise” to begin strengthening the plantar intrinsics, as well as small, controlled amounts of barefoot activity(e.g. running on grass).
Remember, we interviewed Chris McDougall on our podcast a few months ago, take a listen if you have not already!
Foot Short Strengthening Exercise for Injury Prevention
The foot shortening exercise is performed by sitting in a chair with your foot planted normally on the ground, then using only your plantar intrinsic muscles (the ones underneath your arch) to “shorten” your foot and raise your arch.
Here’s the deal:
This can be very tough to learn, since your first instinct is to flex your toes or just roll your ankle outward to accomplish this.
McKeon et al. write that establishing control of this muscle can be difficult, but once you’ve mastered it, you can try doing the short foot exercise while standing or even while balancing on one foot. The authors provide no recommendations on how often to do this exercise, or even how many repetitions you should do—this underscores the fact that these are only preliminary recommendations based on McKeon et al.’s hypothesis.
As for the efficacy of the short foot exercise, McKeon et al. point to a couple of small studies, including a 2010 doctoral thesis by Lindsay Drewes at the University of Virginia.
Drewes found that adding the foot shortening exercise to a standard rehab program for chronic ankle instability resulted in better subjective improvements in foot function among the study’s subjects who included the short foot exercise in their rehab program, though these improvements weren’t measurable through objective measurements, like dynamic balance testing.
The idea of a foot core in addition to your regular core is an interesting proposition, but there’s far too little research on it yet to fully endorse it.
As the focus of research swings back towards the foot, it will be exciting to see what new findings are discovered, but for now, the most you should do is think about trying out the short foot exercise and perhaps incorporating a little bit of barefoot running on grass into your weekly training routine, if you don’t do it already.