functional anatomy of the shoulder

Question 1

functions of muscles: action, agonist, antagonist, stabiliser, synergist

Answer 1

• Action = movt(s) produced when a muscle contracts concentrically in isolation (never usually in isolation though)
  Functions of muscles (muscle coordination)
• Mover (agonist): muscle producing the desired movt by contracting either concentrically (action) or eccentrically
• Antagonist: muscle which must relax (i.e. not contracting) to allow the desired movts to occur
  Stabiliser: muscle that supports a body part so that another muscle will have a firm base from which to act e.g. axioscapular muscles
  Synergist (neutraliser): muscle that eliminates an undesired movt that would otherwise be produced by the mover(s)

Question 2

Function of RC muscles

Answer 2

To provide dynamic stability at the shoulder joint by:

• Taking up slack in the shoulder joint capsule during movt → improved capsular ligament function
• Providing a medial force to the humeral head to accurately position it in the centre of the glenoid fossa during shoulder movt = STABILISER FUNCTION
• Synergist function = to cancel out unwanted rotation