1a. Supraspinatus
Action: Assists deltoid muscle in abducting arm at shoulder joint
Innervation: Suprascapular nerve
1b. Biceps brachii
Action: Flexes forearm at elbow joint, supinates forearm at radioulnar joints, and flexes arm at shoulder joint
Innervation: Musculocutaneous nerve
2a. Rectus femoris
Action: Extend leg at knee joint, and flexes thigh at hip joint
Innervation: Femoral nerve
2b. Biceps femoris
Action: Flexes leg at knee joint, and extends thigh at hip joint
Innervation: Tibial and fibular nerves from sciatic nerve
3a. Rectus abdominis
Action: Flexes vertebral column, compresses abdomen, and flexes pelvis on the vertebral column
Innervation: Thoracic spinal nerves (T7 to T12)
3b. Sternocleidomastoid
Action: Flex cervical portion of vertebral column, extend head at atlanto-occipital joint, flex neck and rotate head
Innervation: Accessory (XI) nerve, C2, and C1
4a. Diaphragm
Action: Contraction and relaxation which affects vertical dimension
Innervation: Phrenic nerve (contains axons from C3 to C5)
4b. External intercostals
Action: Elevates and depresses ribs
Innervation: T2 to T12 spinal nerves