1. Throwing a baseball overhead
- Subscapularis
Action: Arm internal rotation; stabilizes humeral head in glenoid cavity
Innervation: Upper and lower subscapular nerves (C5 - C6)
- 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: Axilliary nerve
2. Kicking a ball
- Psoas major
Action: acting together with the iliacus muscles flex thigh at hip joint, rotate thigh laterally, and flex trunk on hip as in sitting up from supine position.
Innervation: Lumbar spinal nerves L2–L3.
- Gracilis
Action: Adducts thigh at hip joint, medially rotates thigh, and flexes leg at knee joint.
Innervation: Obturator 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.
- Transverse abdominis
Action: Compresses abdomen.
Innervation: Thoracic spinal nerves T8–T12, iliohypogastric nerve, and ilioinguinal 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, which contains 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.
References:
Subscapularis muscle. (2020, February 16). Kenhub. https://www.kenhub.com/en/library/anatomy/subscapularis-muscle
Tortora, G. J., & Derrickson, B. H. (2017). Principles of Anatomy and Physiology (15th ed.). Wiley. Retrieved from https://handoutset.com/wp-content/uploads/2022/05/Principles-of-anatomy-and-physiology-Wiley-2017-Derrickson-Bryan-H._-Tortora-Gerard-J..pdf.