Shoulder impingement happens when the tendons and fluid-filled cushion (bursa) at the top of your shoulder get pinched in a narrow space every time you raise your arm. The pinching occurs between the ball of your upper arm bone and a bony shelf called the acromion that sits above it. This compression irritates the rotator cuff tendons and bursa, causing pain that typically flares between about 70 and 120 degrees of arm elevation, roughly the range where you’d reach for a seatbelt or lift something onto a shelf.
What Gets Pinched and Why It Hurts
The subacromial space, the gap between your upper arm bone and the acromion, is only about a centimeter wide. Packed into that space are four rotator cuff tendons, the long head of the biceps tendon, a connective tissue band called the coracoacromial ligament, and the subacromial bursa. When any of these structures swell from overuse or irritation, the already-tight space gets even tighter. Raising your arm compresses the inflamed tissue against bone, producing that signature arc of pain.
Most people notice the pain is worst in a specific window of motion. Below about 70 degrees of arm lift, the structures aren’t being compressed much. Between 70 and 120 degrees, the pinch is at its peak. Above 120 degrees, the arm bone clears the acromion and pain often eases. This “painful arc” pattern is one of the most reliable signs that impingement is the problem.
What Causes It
There’s rarely a single cause. Impingement usually results from a combination of structural anatomy, movement patterns, and workload on the shoulder.
One factor you can’t control is the shape of your acromion. Acromions come in three shapes: flat, curved, and hooked. A hooked acromion narrows the subacromial space from the start. In studies comparing people with and without impingement, only 2% of healthy controls had a hooked acromion, compared to 20% of people with impingement or rotator cuff tears. That said, plenty of people with hooked acromions never develop symptoms, so bone shape alone isn’t destiny.
Repetitive overhead work is one of the strongest modifiable risk factors. A study of slaughterhouse workers, whose jobs demanded constant forceful shoulder movements, found they were more than five times as likely to develop shoulder impingement compared to workers in less physically demanding roles at the same company. Former slaughterhouse workers had nearly eight times the risk, suggesting the damage accumulates over years. Painters, electricians, swimmers, and anyone who repeatedly lifts their arms overhead faces similar exposure.
Poor shoulder blade mechanics also play a role. When the muscles that stabilize your shoulder blade (especially the serratus anterior, middle trapezius, and lower trapezius) are weak or uncoordinated, the blade tilts or wings out during arm movement. This shifts the acromion downward into the tendons below, effectively shrinking the subacromial space from above.
How It’s Diagnosed
Diagnosis is primarily clinical, meaning a provider can usually identify impingement through a physical exam without imaging. Two tests are used most often. In one, the examiner lifts your arm forward while stabilizing your shoulder blade, compressing the subacromial space. In the other, they bend your arm to 90 degrees and rotate it inward. Both are designed to reproduce your pain by mechanically squeezing the irritated tendons.
These tests are good at catching impingement when it’s present (sensitivity around 74 to 78%), but they’re not great at ruling out other problems (specificity around 57 to 58%). That means a positive test strongly suggests impingement, but your provider may still want imaging if your symptoms are unusual, if you’re not improving, or if a rotator cuff tear needs to be ruled out. An MRI can show tendon damage, bursitis, and the shape of the acromion, while X-rays can reveal bone spurs or acromion type.
What Treatment Looks Like
The cornerstone of treatment is exercise-based rehabilitation, and the evidence strongly supports starting there. Multiple systematic reviews comparing physical therapy to surgery for shoulder impingement have found no meaningful difference in pain, function, range of motion, or strength between the two approaches in the short, medium, or long term. Home-based strengthening programs produce outcomes similar to surgery plus post-surgical rehab.
A typical rehab program focuses on two goals: reducing the irritation and rebuilding the strength and movement patterns that prevent it from returning. Early on, you’ll likely modify activities that provoke pain, apply ice after activity, and begin gentle range-of-motion work. As symptoms settle, the focus shifts to strengthening the rotator cuff (particularly the external rotators) and the muscles that control your shoulder blade. Most people start feeling noticeably better within a few weeks, though full recovery can take several months. Some cases require up to a year of consistent work.
If pain is severe enough to interfere with rehab or daily life, a corticosteroid injection into the subacromial space can provide short-term relief, typically lasting four to eight weeks. Guidelines published in 2025 recommend these injections as an option when other conservative measures haven’t worked, paired with physical therapy or a home exercise program. A repeat injection is reasonable if pain returns, with a minimum gap of two to three weeks between injections, though many providers prefer to wait longer. Injections are a bridge to help you participate in rehab, not a standalone fix.
Surgery, specifically subacromial decompression, involves shaving away bone or tissue to widen the space. It’s typically reserved for people who haven’t improved after several months of dedicated rehab. Given the evidence showing equivalent outcomes, surgery makes most sense when a structural problem like a bone spur or severely hooked acromion is clearly contributing and conservative care has genuinely been exhausted.
Exercises That Help and Why
The muscles that matter most in shoulder impingement aren’t the ones most people think of. The rotator cuff gets the headlines, and it does need attention, particularly the external rotators (teres minor and infraspinatus) that keep the arm bone centered in its socket. Simple resistance band exercises where you rotate your forearm outward with your elbow at your side are a staple of nearly every impingement rehab program.
But the shoulder blade stabilizers are equally important. The serratus anterior, middle trapezius, and lower trapezius work together to tilt and rotate your shoulder blade upward as you raise your arm. When they fire properly, the acromion lifts out of the way and the subacromial space opens up. When they don’t, every overhead reach becomes a pinch. Exercises like wall slides, prone Y-raises, and scapular push-ups target these muscles specifically.
Tightness matters too. A tight pectoralis minor (the smaller chest muscle beneath the one you can see) pulls the shoulder blade forward and tips the acromion down. Stretching this muscle, along with the upper trapezius and levator scapulae on the back of the neck, helps restore normal blade positioning. The combination of stretching what’s tight and strengthening what’s weak addresses the mechanical root of the problem rather than just managing symptoms.
Reducing Risk of Recurrence
Shoulder impingement tends to come back if the underlying movement and strength deficits aren’t corrected. If your job or sport demands repetitive overhead work, building and maintaining shoulder blade and rotator cuff strength is protective. Even 10 to 15 minutes of targeted exercises three times per week can make a meaningful difference once you’ve recovered.
Pay attention to posture during prolonged desk work or driving. A rounded upper back shifts the shoulder blades forward, narrowing the subacromial space in the same way weak stabilizer muscles do. Periodic breaks to pull your shoulders back and perform a few scapular retractions can offset hours of slouching. If your symptoms originally developed from a specific activity, gradually building back into that activity rather than jumping to full intensity gives the tendons time to adapt without re-irritating them.