The traps, short for the trapezius, are a large, flat muscle that spans the back of your neck, shoulders, and upper back. It’s technically one muscle on each side of your spine, but because the fibers run in three different directions, the trapezius functions like three separate muscles stacked on top of each other. Each section moves your shoulder blade in a different way, making the traps essential for nearly every movement involving your arms, shoulders, and head.
Where the Trapezius Sits
The trapezius is one of the most superficial muscles in your back, meaning it sits right beneath the skin. It gets its name from its trapezoidal shape. The muscle originates along the midline of your body, starting at the base of your skull and running all the way down to the middle of your spine (roughly the level of your lowest rib). From there, the fibers fan outward and attach to your shoulder blade and collarbone.
Because it covers such a large area, anatomists divide it into three functional regions: upper fibers, middle fibers, and lower fibers. Each region pulls on your shoulder blade from a different angle, and understanding these three parts explains why the trapezius shows up in so many different movements.
What Each Section Does
The upper traps run from the base of your skull and the back of your neck down to your collarbone. These fibers elevate your shoulder blade (the classic shrugging motion) and help rotate it upward when you raise your arm overhead. They also extend your neck, tipping your head backward. When people talk about carrying stress in their shoulders, it’s the upper traps that are contracting and tightening.
The middle traps attach along the upper spine and run horizontally outward to the shoulder blade. Their job is retraction: pulling your shoulder blades together toward your spine. Think of squeezing your shoulder blades back as if pinching a pencil between them. This action is critical for maintaining upright posture.
The lower traps angle downward from the mid-spine to the shoulder blade. They depress the shoulder blade, pulling it down, and they work with the upper fibers to rotate the shoulder blade upward during overhead reaching. This upward rotation is a team effort. The upper fibers pull the top of the shoulder blade up while the lower fibers pull the bottom edge inward and down, creating a smooth rotational movement without the whole shoulder blade shifting up or sideways.
How the Traps Work With Other Muscles
The trapezius doesn’t act alone. Every time you lift your arm overhead, the three trap regions coordinate with another key muscle called the serratus anterior, which wraps around your rib cage. Together, these muscles form what’s called a force couple: they pull on the shoulder blade from opposite directions to produce controlled rotation. The upper and lower traps cancel out each other’s vertical pull, preventing the shoulder blade from drifting up or down, while the trapezius as a whole and the serratus anterior prevent it from sliding side to side.
This teamwork matters because when part of the system fails, shoulder problems follow quickly. When the trapezius is paralyzed (from damage to the nerve that controls it), people lose the ability to raise their arm past 90 degrees, experience visible shoulder drooping, and develop a characteristic “scapular flip” where the shoulder blade wings outward during arm movement. The middle and lower traps score zero on strength testing in these cases, showing how essential they are for stabilizing the shoulder blade during any arm motion.
Why the Traps Are a Common Source of Pain
The upper trapezius is one of the most pain-prone muscles in the body, particularly for people who work at desks. A study of 305 office workers who spent four or more hours daily at a computer found that 40% had active painful trigger points in their right trapezius, and 35% had them on the left side. Women were affected at roughly double the rate of men, with 54% of women developing trigger points in the right trapezius compared to 25% of men.
These trigger points don’t just cause local shoulder and neck soreness. They refer pain to other areas in a predictable pattern. Pressing on a trigger point in the upper trapezius typically sends pain up the back and side of the neck. In people with chronic tension headaches, that referred pain extends to the temple region. In one study, 45% of chronic tension headache sufferers recognized the pain produced by pressing their upper trap trigger point as the same sensation as their usual headache. Those with active trigger points in the upper traps reported more intense and more frequent headaches than those without them.
Posture and Trap Imbalances
A common postural pattern called upper crossed syndrome illustrates how the three parts of the trapezius can work against each other. In this pattern, the upper traps become chronically tight and overactive while the middle and lower traps become weak and underactive. At the same time, the chest muscles tighten and the deep neck flexors weaken. The result is a recognizable posture: rounded shoulders, a forward head position, and an exaggerated curve in the upper back.
This imbalance develops gradually from prolonged sitting, especially with the arms in front of the body (typing, scrolling, driving). The upper traps stay engaged to hold the head up as it drifts forward, while the middle and lower traps, which should be pulling the shoulder blades back and down, slowly lose their ability to counterbalance. Over time, the tight upper traps contribute to neck stiffness and headaches, while the weak lower traps compromise shoulder mechanics during overhead movements.
Exercises That Target Each Section
Because the three trap regions have different fiber orientations, no single exercise hits them all equally. Electromyography studies measuring muscle activation during various exercises show clear differences in which movements recruit which fibers.
Scapular retraction (pulling the shoulder blades together while holding the arms at roughly 80 degrees of elevation) produced the strongest overall activation, hitting the upper traps at 62% of maximum, the lower traps at 51%, and the middle traps at 50%. It’s an effective all-around trap exercise, but it does favor the upper fibers.
For targeting the lower traps specifically, two exercises stand out. The press-up (pushing your body upward from a seated position using your hands on a surface beside your hips) activated the lower traps at 56% of maximum while keeping the upper traps at only 27%, making it a good choice for building lower trap strength without over-recruiting the upper fibers. Bilateral shoulder external rotation (rotating both arms outward against resistance) produced the best isolation ratio, activating the lower traps at 2.35 times the rate of the upper traps.
These ratios matter for correcting the postural imbalances described above. If your upper traps are already overactive and tight, exercises that preferentially strengthen the lower and middle traps without further loading the upper fibers are more useful than movements like heavy shrugs, which primarily drive upper trap activation.
The Nerve Behind It All
The trapezius is powered by the spinal accessory nerve, the 11th cranial nerve. This is unusual: most muscles in your back are controlled by spinal nerves branching off the spinal cord, but the trapezius gets its motor signals from a nerve that originates in the brainstem. This nerve also controls the sternocleidomastoid muscle on the front of your neck. Sensory information from the trapezius (pain, pressure, stretch) travels through a separate pathway via cervical spinal nerves from the second through fourth vertebrae.
The spinal accessory nerve’s relatively exposed path through the neck makes it vulnerable to injury during surgeries in the neck region, particularly lymph node biopsies. When damaged, the trapezius loses its ability to contract, leading to shoulder blade instability, chronic shoulder pain, visible muscle wasting, and the inability to raise the arm fully. Because the nerve controls the entire trapezius, damage affects all three regions simultaneously.