Everyone says core stability is the key to running healthy and fast, so like many runners you may do a fair amount of core exercise. That will probably make you feel really strong, but it may not translate to fewer leg and foot injuries, faster times, or feeling good.
This is the sort of inconvenient truth that you might brush aside for awhile, thinking the problem is probably something else, like maybe your training plan or your shoes. Or maybe it’s just that your core stability just isn’t good enough yet.
In fact, the opposite is probably true. You almost certainly have too much core stability.
To understand this phenomenon, let’s look at what happens when you run with a perfectly stable core.
Researchers Joseph J. Morley, DC, PhD and Edward Traum, DC, performed three studies looking at what happened to the gait of runners who were put in a cast to hold their pelvis and midsection still and how that compared to running without the cast.
They found roughly nine consequences of an immobilized core in all. Here they are:
Study One: Ground Reaction Force
In their first study they looked at the effect on various components of ground reaction force. Their findings were:
Casted running showed that the initial vertical heel strike maximum was increased (p < .02) and that the anterior–posterior deceleration impulse was increased (p < .01). The maximum vertical ground reaction force was decreased in casted running (p < .01), as was the anterior–posterior acceleration impulse (p < .02).(Morley & Traum, 2016)
What this translates to for the runners is:
- heels hitting the ground harder
- braking more with every footstrike
- less springiness
- less push-off (or ability to push oneself forward)
None of this feels very good or improves performance. In fact, these changes make running feel more like a pounding–the very thing you’re probably trying to avoid.
Study Two: Muscle Activity
In their second study they looked at how casting the core affected muscle activity as measured by EMG. They found:
Casted running resulted in an increase in erector spinae (p < 0.01) and quadriceps femoris (p = 0.02) electromyography activity. Total stride time and swing time of gait were decreased during casted running (p < 0.01), indicating a shift towards shorter and thus more frequent steps to run the same distance. The normal electromyographic data collected was in agreement with previously reported work.(Morley & Traum, 2018)
In other words, when running with an extremely stable core:
- the muscles on either side of the spine worked more
- the largest of the quadriceps muscles worked more
- stride length shortened
If you’ve been having any back soreness or fatigue from running, and/or your quads are the muscles you feel you use the most (and which get the sorest after a marathon), then more core stability is not the thing you need.
Study Three: Energy Use and Center of Mass Movement
In the third study they looked at oxygen consumption–a measure of how much energy you’re using–and vertical movement of the center of mass (or vertical oscillation). They found:
Casted running resulted in an increase in oxygen consumption (p < 0.01). Casted running resulted in less vertical movement of the body’s center of mass (p < 0.01).(Morley & Traum, 2019)
Put simply, when running with the core held still:
- it took more energy
- the runners bounced less
Vertical oscillation has a reputation as something runners should minimize, but it has benefits, and having too little of it is bad for your running.
The bottom line here is that when the core is held almost perfectly still, running gets worse. It’s more work and more pounding. And on top of that, you’re not wearing a cast–you’re actually contracting your core muscles to cause this, which it’s costing you energy to do.
If you’re experiencing any of these effects of too much core stability, then you need to start working on optimizing the action of your core instead. Your running will almost immediately start feeling smoother, lighter, and easier, and you’ll find yourself running faster without trying to. Get my best free resources for improving your core action on this page.