As much as the posture and chairs we use when we sit and the shoes we wear when we run affect our bodies, our sleeping positioning and beds are important as well; after all, most of us spend at least the same amount of time in bed as we do in our office chairs, and probably more hours lying horizontal than running around the track.
The last thing I’m going to tell you is that one particular sleep position is right for everyone. However, there are two sleep positions that can lead directly to problems with your neck and shoulders.
First, sleeping on your stomach is not a position prone to ergonomic approval. Basically, the problem lies with the fact that breathing effectively requires you to turn your head to the side. Because most people will consistently choose the same side, the repeated stress on the same muscles can result in stress on the joints connecting the cervical spine.
As a comparison, imagine that you sit in front of the TV to watch a movie, only the television is not directly in front of you, but directly to either your left or right side. If you didn’t move the rest of your body in order to facilitate viewing, but simply turned your head for the entire 90 minutes or so, you’d be less than comfortable. Well, the ergonomic issues are intensified when you’re doing the same thing to your neck for eight full hours, 
every night.
If you simply cannot fall asleep in any other position, placing pillows under your neck and torso will at least lessen the amount of rotation needed in order to facilitate breathing; alternating sides to which you turn your head can also be a help.
Second, lying on your side with your arms overhead can put undue stress on your weight-bearing shoulder. Often, patients mention that they wrap a pillow around their head and hug it with their arms. This kind of sleep position can cause damage to the downward-facing shoulder by compressing the nerve bundle as it flows into the arm. If you sleep in this position and you’ve experienced waking up with a numb arm or hand, you now know the probable cause.
Another potential issue that can stem from sleeping in a side-lying position is that the head of your humerus can be pushed forward, which prompts risk of impinging the tendons of your rotator cuff. For these reasons, those who have had shoulder injuries can delay recovery by sleeping with their weight on their problem shoulder.
As you experiment with different sleep positions, you may want to evaluate the reason you tend to default to the position that you do. Perhaps it has to do with the location of your window, bedroom door, or partner. Changing the location of your bed or the side on which you sleep can make a major difference in your ergonomics while you sleep.
D.C. Physical Therapist
Dan Baumstark operates a boutique physical therapy office located in the heart of Washington, D.C. Visit his website at www.physiodc.com or set up an appointment by calling 202-223-8500.
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