1. Throwing a baseball overhead
a. Biceps brachii
- Action: Flexes arm at shoulder joint
- Innervation: Musculocutaneous nerve
b. Deltoid
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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
2. Kicking a ball
a. Quadriceps femoris
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Action: All four heads extend leg at knee joint; for rectus femoris muscle, in particular, it flexes thigh at hip joint.
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Innervation: Femoral nerve
b. Sartorius
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Action: Weakly flexes leg at knee joint. Moreover, it weakly flexes, abducts, and also laterally rotates the thigh at hip joint
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Innervation: Femoral nerve
3. Doing sit-ups
a. Rectus abdominis
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Action: Flexes vertebral column (especially the lumbar portion)
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Innervation: Thoracic spinal nerves T7-T12
b. External oblique
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Action: Compress abdomen and flex vertebral column when acting together bilaterally
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Innervation: Thoracic spinal nerves T7–T12 & iliohypogastric nerve
4. Breathing
a. Diaphragm
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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
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Innervation: Phrenic nerve, which contains axons from cervical spinal nerves (C3–C5)
b. External intercostals
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Action: Contraction elevates ribs and increases anteroposterior and lateral dimensions of thoracic cavity, which results in inhalation; relaxation depresses ribs and decreases anteroposterior and lateral dimensions of thoracic cavity, resulting in exhalation.
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Innervation: Thoracic spinal nerves T2–T12
Reference:
Tortora, G. & Derrickson, B. (2017). Chapter 11: The Muscular System. Principles of Anatomy and Physiology (15th ed.). Wiley.