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THE 30-SECOND VERSION
Your shoulder joint can only lift your arm about two thirds of the way. The last third comes from your shoulder blade swinging round. That is why the blade matters.
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HOW IT WORKS
The bone doing a third of the work
No exercise today. Just the arrangement that lets your arm reach the top shelf at all.
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There is a half-used can of deck stain on the top shelf of my garage that I fetched down on Saturday. Nothing remarkable about that, except that I caught sight of myself doing it in the window. I did not simply raise my arm. I rose onto my toes, leaned, and hitched my whole shoulder upward.
On Monday we did a shoulder blade squeeze, and a fair question came to mind afterward. What has my shoulder blade got to do with my shoulder? It sits on my back. The sore part is out at the side.
It turns out they are far more closely tied than that. You can prove it to yourself in about five seconds, sitting where you are.
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QUICK QUIZ · TAP TO ANSWER
Reach across and hold your other shoulder blade. Now raise that arm overhead. What does the blade do?
Try it, then tap what you felt. A ready-to-send reply opens. Just press send and we’ll tell you if you got it right.
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Tingling or Numbness In Your Feet or Hands? (Watch Now)
I’ll get right to the point.
You see, Johns Hopkins University scientists have discovered what could be the TRUE root cause of tingling, itching, and numbness in your feet and hands!
It turns out, there might be a hidden culprit damaging your nerves.
If you suffer from nerve pain, it could be quietly working its way up your legs and arms.
THE MECHANISM |
Two joints, sharing one job |
Here is the thing nobody tells you. The socket your arm sits in is not fixed to your ribs. It is part of your shoulder blade, and your shoulder blade is free to travel across your back. So when you lift your arm, the socket goes along for the ride. |
Researchers worked out the split back in the 1940s, using X-rays and a good deal of patience. Raising your arm straight overhead takes about 180 degrees of movement. Roughly 120 of those degrees come from the ball turning in its socket. The other 60 come from the shoulder blade rotating upward on your ribs. Two parts from the joint, one part from the blade. |
Sit with that for a moment. If your shoulder blade did not move at all, your arm would stop at about 120 degrees. That is somewhere short of a high shelf, and not far enough to comb the back of your hair. Everything above that line is borrowed from a bone on your back. |
And the blade does a second job while it turns. There is a bony roof over your shoulder joint, and the cuff tendons pass underneath it in a narrow gap. As the blade rotates upward, it lifts that roof out of the way. In other words, the blade is not just adding reach. It is clearing a path so the tendons are not squeezed as the arm goes up. |
Which explains Monday |
So that is why a shoulder program bothers with the shoulder blade. The four small cuff muscles keep the ball centered in the socket. The blade muscles move the socket itself. Train one and ignore the other and you have a good crew working from a wobbly platform. |
A caution about that tidy ratio |
Two parts to one sounds beautifully precise, and I have to be straight with you about it. That figure is an average across the whole arc. When researchers measure people carefully, the share changes at different heights, and it varies a good deal between healthy people. Nobody should be trying to hit a number. What clinicians actually look for is whether the movement is smooth and even on both sides. |
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⚠ WORTH GETTING LOOKED AT
When the movement itself looks wrong
Small differences between sides are ordinary. These are worth a doctor or therapist:
● A shoulder blade that sticks out noticeably from your back on one side, or new weakness in the arm.
● An arm you cannot raise at all, especially after a fall, or pain that came on suddenly.
● Shoulder pain with chest tightness, sweating, or shortness of breath. That needs emergency care.
When in doubt, get it checked. PainFree adds to your doctor’s care. It never replaces it.
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THIS WEEK’S QUICK WINS
Three ways to use what you just learned
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🪨 Compare your two sides in a mirror
Stand with your back to a mirror, look over your shoulder, and raise both arms slowly. Smooth and matching is what you want. A shoulder that hitches up early, or a blade that lags, is worth mentioning to a therapist.
1 minute • Look for smooth, not perfect
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📦 Lower the top shelf
The things you reach for daily do not need to live above your head. Move the everyday items down to chest height and leave the high shelf for the paint you touch twice a year.
One afternoon • Pays back daily
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🦵 Keep the blade squeeze going
Now you know what it is for. The blade is the moving platform your arm works from, and a third of your reach depends on it turning properly. Ten squeezes while the kettle boils.
1 minute • The base under everything
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One hundred and twenty, plus sixty
The arrangement was described in the 1930s and measured properly by Inman and colleagues in 1944, using X-rays to track the bones as the arm rose. Of roughly 180 degrees of elevation, about 120 come from the ball-and-socket joint and about 60 from the shoulder blade rotating upward against the ribs. Take the blade’s share away and the arm stalls near 120 degrees. The blade’s turn also raises the bony roof above the joint, giving the cuff tendons room to pass. Where I have to be careful is the tidiness of it. Later measurements show the share shifts through the arc and differs between healthy people, so it is a useful average rather than a target to hit.
| 120° comes from the ball turning in its socket |
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| 60° comes from the shoulder blade rotating on your ribs |
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| 1934 when a surgeon first described the partnership |
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A third of your reach is not your shoulder at all. It is a bone on your back, turning at the right moment.
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WHAT THE EVIDENCE SAYS
Three ways people act on this, graded
Training the blade alongside the cuff Sensible, and standard in rehab programs. The cuff centers the ball, the blade muscles move the socket. Both belong in the same plan. |
Having someone watch you move More useful than a number. Clinicians judge this by watching for smooth, even movement on both sides rather than measuring degrees. |
Chasing a perfect two to one ratio Not a goal worth having. The real share varies through the movement and between healthy people. Smooth beats mathematically correct. |
A physical therapist can watch how your shoulder moves in a single visit, which is worth more than any self-assessment.
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WORTH KNOWING
One bone
Your shoulder blade has no bony joint with your ribs or your spine at all. It floats on a bed of muscle, and its only hard connection to the rest of your skeleton is your collarbone. That is how a whole arm hangs off you, and why muscle is the only thing keeping the platform steady.
Basic shoulder anatomy.
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QUICK POLL · TAP TO ANSWER
Can you reach the top shelf comfortably?
It tells us where to aim the rest of shoulder week. Just press send.
We read every reply.
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