1. Throwing a baseball overhead
> Deltoid
Action: Lateral fibers abduct arm at shoulder joint; anterior fibers flex and medially rotate arm at shoulder joint; posterior fibers extend and laterally rotate arm at shoulder joint
Innervation: Axillary nerve
> Subscapularis
Action: Medially rotates arm at shoulder joint
Innervation: Upper and lower subscapular nerve
2. Kicking a ball
> Biceps femoris [Hamstrings]
Action: Flexes leg at knee joint and extends thigh at hip joint
Innervation: Tibial and fibular nerves from sciatic nerve
> Vastus intermedius [Quadriceps]
Action: extend leg at knee joint
Innervation: Femoral nerve
3. Doing sit-ups
> Rectus abdominis
Action: Flexes vertebral column, especially lumbar portion, and compresses abdomen to aid in defecation, urination, forced exhalation, and childbirth. RMA: Flexes pelvis on the vertebral column.
Innervation: Thoracic spinal nerves T7–T12
> External oblique
Action: Acting together (bilaterally), compress abdomen and flex vertebral column; acting singly (unilaterally), laterally flex vertebral column, especially lumbar portion, and rotate vertebral column
Innervation: Thoracic spinal nerves T7–T12 and the iliohypogastric nerve
4. Breathing
> Diaphragm
Action: Contraction of diaphragm causes it to flatten and increases vertical dimension of thoracic cavity, resulting in inhalation; relaxation of diaphragm causes it to move superiorly and decreases vertical dimension of thoracic cavity, resulting in exhalation
Innervation: Phrenic nerve (axons from cervical spinal nerves (C3–C5))
> Internal intercostals
Action: Contraction draws adjacent ribs together to further decrease anteroposterior and lateral dimensions of thoracic cavity during forced exhalation
Innervation: Thoracic spinal nerves T2–T12