Muscle compartments

Anterior neck:

• Prime mover (anterior): Sternocleidomastoid** → flexes neck; rotates head.

  • Synergist: Scalenes.

Posterior neck:

Posterior: Splenius capitis / cervicis** → extends head/neck; rotates head.

Anterior trunk:

• Prime mover (anterior): Rectus abdominis** → flexes vertebral column.

  • Synergist: External & internal obliques → assist in trunk flexion.

Posterior trunk:

Posterior: Erector spinae** → extends vertebral column.

Anterior arm (shoulder to elbow):

• Prime mover (anterior): Brachialis** → flexes forearm.

  • Synergist: Biceps brachii → assists flexion; supinates forearm.

Posterior arm (shoulder to elbow):

Posterior: Triceps brachii** → extends forearm.

Anterior Forearm (Elbow to fingers):

• Prime mover (anterior): Flexor carpi radialis → flexes wrist.

• Digitorum → flexes digits.

  • Synergist: flexor digitorum superficialis → assists in flexion of digits.

Posterior forearm (Elbow to fingers):

Posterior: Extensor digitorum → extends wrist and digits.

Anterior shoulder:

• Prime mover (anterior): Deltoid → flexes and medially rotates arm.

  • Synergist: Coracobrachialis → assists in arm flexion.

Posterior shoulder:

Posterior: Deltoid → extends and laterally rotates arm.

Anterior hip (hip → knee):

• Prime mover (anterior): ilioposas → flexes thigh at hip.

  • Synergist: Rectus femoris → assists in hip flexion.

Posterior hip (hip → knee):

Posterior: Gluteus maximus → extends thigh at hip.

Anterior thigh (knee):

• Prime mover (anterior): Quadriceps femoris → extends leg at knee.

  • Synergist: Rectus femoris → knee extension.

Posterior thigh (knee):

Posterior: Biceps femoris → flexes leg at knee.

Anterior leg (leg → ankle):

• Prime mover (anterior): Tibialis anterior → dorsiflexes foot & extends digits.

  • Synergist: Extensor digitorum longus → assists in dorsiflexion & digit extension.

Posterior leg (leg → ankle):

Posterior: Gastrocnemius/soleus → plantar flexes foot.

Supraspinatus (OIAA)?

• Origin: Rotator cuff muscle

• Insertion: Greater tubercule of humerus.

• Action: Abducts and stabilizes humerus.

Infraspinatus (OIAA)?

• Origin: Rotator cuff muscle

• Insertion: Greater tubercule of humerus.

• Action: Lateral rotation of humerus.

Teres minor (OIAA)?

• Origin: Rotator cuff muscle

• Insertion: Greater tubercule of humerus.

• Action: Lateral rotation of humerus.

Subscapularis (OIAA)?

• Origin: Rotator cuff muscle

• Insertion: Greater tubercule of humerus.

• Action: Medially rotates arm.

SITS Rotator cuff muscles:

Supraspinatus

Infraspinatus

Teres minor

Subscapularis