2 doctors weighed in:

Why are there 7 shoulder extensor muscles?

2 doctors weighed in
Dr. Theodore Shybut
Sports Medicine
1 doctor agrees

In brief: Best bet: evolution

The posterior deltoid, latissimus dorsi, teres major are shoulder extensors.
Other muscles with extension moments include subscapularis, long head of triceps, infraspinatus, teres minor, sternal head of pectoralis major. Presumably shoulder muscles evolved to facilitate independent use of the upper extremities for fine motor tasks (allows me to type this answer) in upright biped organisms.

In brief: Best bet: evolution

The posterior deltoid, latissimus dorsi, teres major are shoulder extensors.
Other muscles with extension moments include subscapularis, long head of triceps, infraspinatus, teres minor, sternal head of pectoralis major. Presumably shoulder muscles evolved to facilitate independent use of the upper extremities for fine motor tasks (allows me to type this answer) in upright biped organisms.
Dr. Theodore Shybut
Dr. Theodore Shybut
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