Kinesiology THURSDAY – Bicep Long Head v Infraspinatus (Tug-o-War Series)

Illustration of human shoulder and arm muscles.

Ever have a patient exhibit pain and/or weakness with resistance to shoulder flexion or external rotation? We all have. It is one of the most common symptoms associated with rotator cuff tendonitis or impingement.

The battle between infraspinatus and the biceps long head is one you won’t find in anatomy books but exists in the real world and their story lies in the common trigger points marked by the “x” above. Remember, trigger points appear in muscles that are chronically short. And here is the story they may tell:

A trigger point in the inferior angle of the infraspinatus would indicate a scapula that is upwardly rotated. This may be confirmed if there is a coinciding upper trapezius trigger point.
If the scapula is upwardly rotated, this will place the bicep long head tendon in a long/weak position.
A trigger point in the bicep long head muscle belly may downwardly rotate the scapula, placing the infraspinatus in a long/weak position.

One way to test and fix shoulder flexion weakness:

Manual muscle test (MMT) shoulder flexion. If weak or painful, check for infraspinatus trigger point.
Perform deep trigger point massage for 30-60 seconds
Re-test shoulder flexion.

One way to test and fix shoulder external rotation weakness:

MMT shoulder external rotation. If weak or painful, check for bicep long head trigger point
Perform deep trigger point massage for 30-60 seconds. Longitudinal strokes work best.
Re-test shoulder external rotation

You just might be surprised to find pain-free strength is restored in one of these agonists when trigger point is released in the antagonist.

An exercise fix idea:

If infraspinatus trigger point release corrected shoulder flexion weakness, then add rhomboid exercise prior to shoulder flexion strengthening to encourage scapular downward rotation.
If bicep trigger point release corrected shoulder external rotation weakness, then add triceps exercise prior to shoulder ER strengthening. Here’s a video with some ideas and some great music.

Notice how the recommendations are activating another antagonist of the tight muscle to inhibit it. Now, that’s some exciting stuff!

Why does this matter?

If shoulder flexion and/or external rotation motion is weak because it is painful, don’t rely on strengthening the weak motion to fix the problem. Instead, hunt down a trigger point in the functional antagonist and fix what you find.

Because nobody has time to be in pain.

Until next time…