Does Sleeping on Your Side Cause Shoulder Pain?

Almost everyone with a sore shoulder reports that it is worse at night, and many conclude their sleeping position caused it. The research on that question turns out to be harder to read than it first appears.

Here is what each study found, why they disagree, and what is actually worth doing about a shoulder that hurts at night.

The study that seems to settle it

A 2024 case series published in Arthroscopy, Sports Medicine, and Rehabilitation looked at a consecutive series of 58 patients seen between July and December 2019, all with a significant rotator cuff tear confirmed by ultrasound, MRI, or both. The tears were either partial-thickness involving more than half the tendon, or full-thickness.

Of those 58 patients, 52 were side sleepers. Four were stomach sleepers, one was a back sleeper, and one reported no preference among the three positions. The statistical test returned a p-value below 0.0001, and the authors concluded that a relationship exists between side-sleeping preference and the presence of a rotator cuff tear.

Read on its own, that looks conclusive. Nearly 90 percent of people with a torn rotator cuff slept on their side.

Why that number does not mean what it looks like

The problem is that the study describes no control group of people without rotator cuff tears.

Side sleeping is the most common sleep position in the general population. If you take any group of people, most of them will be side sleepers, whether they have a shoulder problem, a knee problem, or nothing at all. Without a comparison group, a finding that 52 of 58 patients sleep on their side does not tell you whether that rate is higher than in people with healthy shoulders.

This is a general limitation of case series rather than a criticism of the researchers, who reported what they found in the patients in front of them. It is the interpretation that needs care.

The larger study that found the opposite

A 2018 cross-sectional study published in BMC Musculoskeletal Disorders examined 761 workers across 15 employers in Wisconsin, Utah, and Illinois, using questionnaires, structured interviews, physical examinations, and body diagrams.

Shoulder pain at the main shoulder joint was present in 36.4 percent of participants, and rotator cuff tendinopathy in 18.0 percent.

The results ran opposite to what the researchers expected. Compared with sleeping on the back, the freefaller position was associated with lower odds of shoulder pain, with an odds ratio of 0.59 and a confidence interval from 0.36 to 0.95. In other words, that position looked protective. For rotator cuff tendinopathy specifically, no sleep position showed a significant association at all.

The explanation that reconciles both

The 2018 authors offered an interpretation that makes sense of the whole picture. People who already have shoulder pain, they suggest, may have learned to avoid sleeping in the position that provokes it.

Think about what that does to a study conducted at a single point in time. Everyone who finds a position painful has already stopped using it. When researchers then ask people what position they sleep in, the painful position appears under-represented among people with pain, and therefore looks protective.

This is reverse causation, and it is very difficult to escape in cross-sectional research. The authors stated directly that this kind of design cannot establish causality and recommended longitudinal studies, which would follow people over time and see who develops symptoms.

So the two studies are less contradictory than they first appear. One found an association without a comparison group. The other found an association in the opposite direction with a plausible explanation for why. Neither establishes that a sleeping position causes shoulder damage.

Why shoulders hurt more at night regardless

Night pain is one of the most consistently reported features of shoulder problems, and this part is not really in dispute.

Several contributors are commonly described. Lying down changes the position of the arm relative to the shoulder joint and removes the gentle traction that gravity provides when you are upright. There are fewer distractions at night, so pain that was in the background all day becomes the main thing you notice. And sustained pressure on one side loads the structures of that shoulder for hours without the small position changes that happen constantly while awake.

Night pain features across a range of shoulder conditions, including the ones covered in our guides to frozen shoulder and rotator cuff problems and shoulder bursitis versus tendinopathy. It is a symptom worth reporting to whoever assesses you, because it helps characterise the problem, though it does not by itself identify which structure is involved.

What is actually worth doing

Adjusting your sleeping position is worth doing for sleep quality and comfort. Sleep matters for recovery generally, as covered in our piece on sleep and injury risk, and lying awake with a sore shoulder helps nothing.

Practical approaches people find useful include sleeping on the unaffected side with a pillow in front supporting the sore arm, sleeping on the back with a small pillow or folded towel under the upper arm to stop it dropping backward, and avoiding sleeping with the arm up overhead. None of these are backed by strong trial evidence, so treat them as comfort strategies to try rather than prescriptions. Give one a week or two before judging it.

What is worth avoiding is the conclusion that the mattress or the pillow is the whole problem. Buying new bedding is a reasonable thing to do if the old set is uncomfortable, and it is an expensive way to postpone finding out what is happening inside the shoulder.

When to get it looked at

Shoulder pain that wakes you regularly and has not settled over a few weeks is worth having assessed. Night pain is one of the most common reasons people finally seek help for a shoulder, often after months of adjusting positions and hoping it resolves.

Some situations need prompt medical attention rather than a physiotherapy booking: shoulder pain with fever, unexplained weight loss, or a history of cancer, an inability to lift the arm at all following an injury, or a shoulder that looks visibly out of shape after trauma. Shoulder or arm pain accompanied by chest pain, breathlessness, sweating, or nausea is a call to 911 rather than a clinic.

If your shoulder has been waking you and changing sides has stopped helping, book a 30-minute assessment and we will work out what is actually driving it. You can see what we treat or reach the clinic here.

This article is general information, not personal medical advice. A regulated practitioner can confirm whether the patterns described apply to you.

Sources

• Is sleep position associated with glenohumeral shoulder pain and rotator cuff tendinopathy: a cross-sectional study (BMC Musculoskeletal Disorders, 2018)
• Rotator Cuff Tears Are Related to the Side Sleeping Position (Arthroscopy, Sports Medicine, and Rehabilitation, 2024)
• College of Health and Care Professionals of BC public registry

This article is for general information only and does not constitute medical advice, diagnosis, or treatment. Individual presentations vary, and assessment findings and treatment plans differ from person to person. If you are experiencing severe symptoms, neurological changes (numbness, weakness, bowel or bladder changes), or a significant trauma, contact your physician or emergency services. Care at Medstar Sport Physio & Health is provided by practitioners registered with their respective British Columbia regulatory colleges.