It's a term that gets thrown around a lot on the internet—including here on STACK.com—but do you actually know what it means? While you may have some idea, learning the definition and function of stabilizer muscles can make you a more knowledgeable gym-goer and help you get the most out of your workouts.
What are Stabilizer Muscles?
Stabilizer muscles work to stabilize the body and its extremities during multi-plane movement. During an exercise, there are primary movers and stabilizer muscles. The primary movers are the muscles doing the majority of the work—they're what's moving the load and they're likely where you'll feel the exercise the most. While the stabilizer muscles aren't directly involved with moving the load, they work to keep certain parts of the body stable and steady so the primary movers can do their jobs efficiently.
While no one muscle is a stabilizer muscle 100 percent of the time (since it's more of a role than a persistent state), certain muscles work as stabilizer muscles much more frequently than others. The rear deltoids, for example, are rarely the primary mover in an exercise but frequently act as a stabilizer during movements that involve the shoulders.
"The rear delts act as a main stabilizer when your elbows come parallel to or behind your body," explains Rick Scarpulla, strength coach and owner of Ultimate Advantage Training.
For example, though the primary movers of the Bench Press are the pectoralis major and the triceps brachii, the rear delts act as a stabilizer muscle to help you control and decelerate the bar effectively. Stabilizer muscles can serve several different roles, but they often work to restrict the movement of certain joints.
"Muscles are designed to work in collaboration with each other to help produce coordinated movement during exercise. Stabilizer muscles do just what their name implies in that they help stabilize joints and parts of the body so that movement patterns are efficient in a kinematic sense," says John Mikula, CSCS and a consultant through Tactical Speed and Strength.
Why are Stabilizer Muscles Important?
Stabilizer muscles are important for several reasons.
Most importantly, they allow us to move efficiently and with good biomechanics. The Barbell Back Squat is a good example. While the quadriceps, hamstrings and gluteus maximus are doing the majority of the work to move the load, the abductor muscles (particularly the gluteus medius) must work to keep the hips and thighs stable. If they're underdeveloped or inactive, that can lead the knees to collapse inwards—a common compensation that makes the exercise both less effective and more dangerous.
"From a functional perspective, inefficient stabilization forces during exercise cause the body to try and accommodate during movement by generating momentum and/or creating adapted movement patterns to try and overcome this lack of stabilization somewhere along the path of the integrated, muscular system," Mikula says.
Stabilizer muscles also allow us to utilize greater loads during our training. While we might not think of the Military Press as a lower back exercise, the muscles in our lower back must work to keep our trunk stable as we move the load overhead. If they're not up to the task, it doesn't matter how strong the primary movers of the exercise are—the movement will be dysfunctional and you won't be able to apply as much force as you could've. "More stable structures have the potential to generate more force and subsequently more power," Mikula says.
Stabilizer muscles spread the work of training and movement throughout our bodies instead of putting all the stress onto one or two primary movers. Not only does this allow us to be more powerful, efficient athletes, but it also prevents those primary movers from getting overworked (which can lead to strain or injury). Essentially, stabilizer muscles make movements—both inside and outside the weight room—safer and more efficient.
What's the Best Way to Strengthen Stabilizer Muscles?
Working out with free weights is a surefire way to strengthen your stabilizer muscles. The same cannot necessarily be said for machines.
In a study from Illinois State University, researchers measured the amount of muscle activity among participants who performed a machine Bench Press and a free weight Bench Press. The loads were identical, and the difference in muscle activity in the primary movers (the pecs and triceps) was statistically insignificant. However, the anterior and medial deltoids exhibited significantly more muscle activity during the free weight Bench Press—an average of 50 percent and 33 percent more activity, respectively—when participants were lifting 60 percent of their one-rep max.
"Higher IEMG values for the anterior and medial deltoid muscles suggest that shoulder stabilizing muscles are more active during the Bench Press performed using free weights compared to a machine," the study stated. Machines don't recruit stabilizing muscles the way free weights do since they often require you to move a load in just one plane of motion. With free weights, the load is free to go anywhere. Stabilizer muscles therefore must work to make sure the load is being controlled and moved efficiently—a job that simply isn't required when working on most machines.