Deep core-muscle weakness in runners leads to compensation strategies that increase pressure and loading on the spine, which may increase the risk of low back pain, a new analysis demonstrates.
Study author Ajit Chaudhari, PhD, FACSM, professor of physical therapy at The Ohio State University, notes that, from the clinical perspective, there’s long been a sense of a relationship between core strength and back problems. This study, published in the Journal of Biomechanics, provides preliminary biomechanical evidence to support that idea, he says.
Using motion capture and force plates to collect data on 8 healthy participants as they jogged around a track, Chaudhari created responsive computerized models of each participant’s musculature. He then isolated and weakened particular muscles for the individual models, and looked at how the model compensated for those changes. The simulation program, developed in 2016 by Chaudhari and first author Margaret Raabe, PhD, is designed to find the most efficient mechanical solution that would maintain the same running form.
“The question we were asking is, what if the deep core muscles were weak, but the person wanted to run the exact same way?” Chaudhari says. “What other muscles would have to compensate to keep the same running kinematics?”
Through the simulations, Chaudhari found that superficial core muscles tended to be recruited to compensate for deep-core weakness. Those muscles are farther from the spine, which means they pull on the vertebrae from farther away, he says. That increases pressure on the spine.
When all deep core muscles were weak, spinal loading increased 15% on the L1 vertebra and 8% on L2 vertebra, according to the simulation. When only the deep muscles of the erector spinae, which extend up the spine, were weakened, the spinal loading increased 11% on the L1 vertebra and 6% on the L2 vertebra.
“We don’t have lot of data to know how much loading is a safe amount,” Chaudhari says, “but we know it can cause damage to the spine.”
Moreover, superficial core muscles that are seen to compensate for deep-core weakness become fatigued faster, he says. “It could mean that running form would change faster,” Chaudhari says.
However, because the simulation was designed to maintain the running form and kinematics of each subject, researchers were unable to look for those potential changes.
The findings confirmed what clinicians observe about low back pain, says Michael Fredericson, MD, professor of orthopedic surgery at the Stanford University Medical Center: “For a back problem these days, you’re going to get some core exercises.”
Fredericson stressed that, because this study was based on computer modeling, it can’t provide complete evidence of the relationship. “It’s a way to give you an idea if that type of modeling makes sense theoretically, and if it does, it gives you the evidence to go ahead with a more clinical study.”
Chaudhari agrees, noting that this analysis was just an initial step, and that clinical work will follow. “The next step is to fatigue people’s muscles and see how they respond,” he says.
If core fatigue and subsequent weakness lead to changes in running kinematics that are harmful, which the simulation didn’t look at, that may be an indication that maintaining form is a good way to prevent pain or injury, he says. If, however, kinematics does not change, the emphasis may need to be on developing strength to prevent fatigue.
“We’re looking to see what we should be using to train people going forward,” Chaudhari says.
Raabe ME, Chaudhari AMW. Biomechanical consequences of running with deep core muscle weakness. J Biomech. 2018;67:98-105.