1. Throwing a baseball overhead
Muscle: 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
Muscle: Pectoralis major
Action: As a whole, adducts and medially rotates arm at shoulder joint; clavicular head flexes arm, and sternocostal head extends flexed arm to side of trunk.
Innervation: Medial and lateral pectoral nerves
2. Kicking a ball
Muscle: Rectus femoris
Action: All four heads extend leg at knee joint; rectus femoris muscle acting alone also flexes thigh at hip joint.
Innervation: Femoral nerve
Muscle: Gluteus maximus
Action: Extends thigh at hip joint and laterally rotates thigh; helps lock knee in extension. RMA: Extends torso
Innervation: Inferior gluteal nerve.
3. Doing sit-ups
Muscle: Rectus abdominis
Action: Flexes vertebral column, especially lumbar portion. RMA: Flexes pelvis on the vertebral column
Innervation: Thoracic spinal nerves T7–T12
Muscle: 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
Muscle: 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, which contains axons from cervical spinal nerves (C3–C5).
Muscle: 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.
Muscle: External intercostals
Action: Contraction elevates ribs and increases anteroposterior and lateral dimensions of thoracic cavity, resulting in inhalation; relaxation depresses ribs and decreases anteroposterior and lateral dimensions of thoracic cavity, resulting in exhalation.
Innervation: Thoracic spinal nerves T2–T12.
Reference: Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy & physiology. Fifteenth edition; Wiley Loose-Leaf Print Companion. Hoboken, New Jersey, John Wiley & Sons, Inc.