Lying external rotator cuff.

Posted by & filed under Exercise and Training.

One of the mysteries of the body, for me, is how puny the external rotator cuff muscles of the shoulder are in comparison with the internal rotators.  Three small muscles rotate the upper arm bone backwards: the infraspinatus, the teres minor and the rear delt.  Five muscles rotate the upper arm bone inwards: the subscapularis, the teres major, the front delt,the pec major and the lats.  Both the pec major and the lats are big muscles!  To counterbalance the strong inward pull from those five muscles, doing some work on the external rotating muscles can help prevent injury and increase upper body strength.

The muscles are clearly labelled. Interesting how big the radial nerve is. I have been to a dissection day – and the smell of formaldehyde is quite overpowering! Much nicer as a photo, even if we can’t get our hands in there.

Any movement that turns the upper arm bone outwards will engage the external rotators of the shoulder.  This particular exercise is a good starting place.  The above video give the gist of the exercise.  Here are a couple of slight changes that will improve things.

  • Lie on your side, with your head supported on something.  Please.  Otherwise various muscles of the neck, for example the scalenes and the SCM will get in a fearful bother and end up in trips to the pain menders.  You do not have to teeter on a bench, the floor is just fine.  Put your head on pillows or a cushion, or a rolled up towel if in the gym.
  • Put a small rolled up towel into the upper armpit, so there is a slight sense of space in the ‘pits and the shoulder does not feel collapsed into the body.  Bring the elbow to the waist and slightly squeeze the back of the armpit onto the towel.  This helps stabilise the shoulder joint.  We are going to turn the upper arm bone outwards, not waggle the whole shoulder blade about.
  • Holding a small weight in that top hand, lower the hand towards the belly button as far down as it will sensibly go.  There is no movement with the shoulder blade itself.
  • Slightly lift the dumbbell away from the lowest point, completely relax the shoulder, then lift the dumbbell up as far as it will sensibly go.  As the exercise progresses, you should get a burning sensation in the back of the shoulder blade.  A burning any where else shows that other muscles are trying to do the job of the external rotator cuff.
  • Lower the dumbbell more slowly than you lifted it up.

This latter remark is very important.  One of the most important actions of the external rotator cuff is to brake the arm at the end of movement – to stop the arm flying out of its socket at the end of a punch.  This is an eccentric contraction, so the muscle must be strong as it lowers the weight – the eccentric part of the action.

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