The term “trunk” might seem outdated, but it holds the key to developing natural, resilient running, and to cultivating our innermost powers of coping with healthful, stimulating kinds of stress. Who doesn’t want a healthy flow of energy coursing through their pelvis, stomach, and spine? Who doesn’t want a strong, resilient backbone, ready and able to engage life fully?

Something to See

It’s widely speculated that the trunk should remain constantly still, in a permanent state of contraction throughout the running cycle. At first glance, it might appear this way when the bare torso of an international athlete is on display. It certainly looks as if the trunk barely moves. But if you look deeper you can observe the fact that years of practice and focusing on technique have made them adept at coordinating the muscles around their trunk and pelvis. So they contract and relax in perfect rhythm with the muscles producing force in their legs. 

I love watching Eliud Kipchoge flash his magnanimous smile and run from his belly to taper the muscular effort in his legs and feet. He uses almost all pelvic rhythm to quicken his leg rate. It’s like revolutions per minute. Of course, it’s a rarity to find an ordinary runner with a specialized, functional physique resembling a world-class runner. But people with normal, everyday bodies can still benefit from their genius.

Core Action

Your trunk is actually a vital part of your “spring system.” It’s massive muscle groups and powerful ligaments contain a surprising number of elastic fibers. Along with the arches of your feet and the flexing of your knees, they absorb the impact of your feet hitting the ground and then spring it back to propel you forward. Using the trunk muscles in the torso to gently tip the pelvis from side to side like a seesaw returns elastic energy to the arch and spring ligaments in the feet. This allows everything to rebound reflexively, pushing you off the ground towards floating, flying and weightlessness. (1) 

Trunk training helps you harness your spring system to increase your stride length without over-reaching. The brilliant Feldenkrais practitioner, Jae Gruenke, founder of The Balanced Runner chooses the words “core action” instead of “core stability” to describe this phenomenon.

Core stability acts like orthotics for your torso. Continually pulling your belly in when you run interferes with your breathing and the proper use of your glutes. And it wastes energy. – Jae Gruenke

Any way you slice it, a well-trained trunk has a soothing effect on your legs. It helps to adjust your foot-strike naturally and eliminates the continuous pounding on your knees from over-striding/heel-striking and iliotibial band syndrome. (2) Once you feel the power of a harmonized spring system, you’ll see why training regimens that “blast your core” without coordinating the legs and feet are missing the mark.

Acknowledgments

(1), (2) Core Stability is Like Orthotics for your Torso – by Jae Gruenke