1. Throwing a baseball overhead
Muscle: Deltoid
Action: Lateral fibers cause abduction; anterior fibers flex and medially rotate arm; posterior fibers extend and laterally rotate arm.
Innervation: Axillary nerve.
Muscle: Subscapularis
Action: Medially rotates arm at shoulder joint.
Innervation: Upper and lower subscapular nerve.
2. Kicking a ball
Muscle: Biceps femoris
Action: Flexes leg at knee joint and extends thigh at hip joint.
Innervation: Tibial and fibular nerves from sciatic nerve.
Muscle: Gluteus maximus
Action: Extends thigh at hip joint and laterally rotates thigh. Extends torso during RMA.
Innervation: Inferior gluteal nerve.
3. Doing sit-ups
Muscle: Rectus abdominis
Action: Flexes vertebral column and compresses abdomen. Flexes pelvis during RMA.
Innervation: Thoracic spinal nerves T7–T12.
Muscle: Iliopsoas
Action: Psoas major and iliacus muscles acting together flex thigh, rotate thigh laterally, and flex trunk on hip as in sitting up from supine position.
Innervation: Lumbar spinal nerves L2–L3.
4. Breathing
Muscle: Diaphragm
Action: Contraction causes it to flatten and increase vertical dimension of thoracic cavity (inhalation); relaxation of diaphragm causes it to move superiorly and decreases vertical dimension of thoracic cavity (exhalation).
Innervation: Phrenic nerve, which contains axons from cervical spinal nerves (C3–C5).
Muscle: External intercostals
Action: Contraction elevates ribs and increases anteroposterior and lateral dimensions of thoracic cavity (inhalation); relaxation depresses ribs and decreases anteroposterior and lateral dimensions of thoracic cavity (exhalation).
Innervation: Thoracic spinal nerves T2–T12.