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Forget core stability — work on your core action to improve running performance

Running form expert Jae Gruenke explains core action and why it's important to runners

Runners are constantly told they need a stronger, more stable core if they want to run well and avoid injuries, but Jae Gruenke of The Balanced Runner says this does a disservice to runners. She coined the term “core action” to describe the relationship between your core muscles and your running form. We sat down with her to talk about what core action means and why core stability is an often misunderstood and misused term.

What’s wrong with “core stability?”

Gruenke says the term core stability emerged from research by Hodges and Richardson in the 1990s on the activity of the transverse abdominis (a deep abdominal muscle) in people with low back pain. It’s defined as “the ability to maintain equilibrium and control of your spine and pelvic region during movement without compensatory movement just within physiological limits.”

Foam roller core routine with Kate Van Buskirk

Although this early definition didn’t mean “static”, Gruenke says many runners and even sports medicine practitioners have interpreted it to mean “hold the core still”. This, she says, hurts runners because it encourages you to immobilize your torso, rather than allowing it to move naturally, as it should during movement. She cited a series of studies by Morley and Traum (2016, 2018, 2019) to illustrate her point.

“They compared runners running normally vs. with a cast immobilizing the pelvis and lumbar area. When casted, the runners — effectively running with partially fused torsos like action figures — had higher oxygen consumption, less vertical movement, more activation of the spinal extensors and rectus femoris (a quadriceps muscle), a stronger heelstrike, shorter strides, and more braking with each footstrike.”

She says runners who try to immobilize their torso hurt their performance even more because, in addition to the effects shown in the studies, it requires considerable additional muscular effort to contract the core muscles to prevent movement. This can also result in excessive stress and ultimately injury to the legs or feet, and running that feels laboured and mechanical.

What is core action?

Instead of trying to hold your torso still when you’re running, Gruenke says runners should be trying to optimize the function of their core. This includes the counter-rotation of your pelvis and lumbar spine to your thoracic spine, which allows you to shift your weight from one leg to the other as you run. The size of this movement varies with speed, terrain, how warm and/or fatigued a runner is, and even whether they’ve reached their current speed by accelerating or decelerating. This is a completely natural movement and shouldn’t be done on purpose.

“It is, however, something a runner should absolutely not try to prevent,” says Gruenke. “And improving overall coordination — a.k.a. running form — improves the ability of a runner’s nervous system to supply the right amount of this movement in each situation.”

How can you improve your core action?

Instead of working on core stability, Gruenke says runners should focus on improving motor control. For some, improvement is as simple as no longer preventing your core — your pelvis and waist and ribcage — from moving. This means abandoning exercises that force you to hold your core still while you move your legs (like planks and clamshells… we know, we’re shocked too).

To help runners improve their core action, Gruenke has created several tools and guides on her website that teach core action and the whole-body context that makes it work. You can check out her website, The Balanced Runnerfor more information.

Work your core like 4-time Olympic champion Mo Farah

“You’ll know your core action is improving when your running feels smoother and easier but actually, when you look at your watch, turns out to be faster,” says Gruenke. “You’ll know it’s better when your legs are less sore and stressed and your breathing is better. You’ll know it’s better when you start feeling like a kid again.”

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