1. Throwing a baseball overhead
Muscle 1: 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 2: Subscapularis
- Action: Medially rotates arm at shoulder joint
- Innervation: Upper and lower subscapular nerve
2. Kicking a ball
Muscle 1: Rectus femoris
- Action: Extend leg at knee joint; rectus femoris muscle acting alone also flexes thigh at hip joint
- Innervation: Femoral nerve
Muscle 2: Biceps femoris
- Action: Flexes leg at knee joint and extends thigh at hip joint
- Innervation: Tibial and fibular nerves from sciatic nerve
3. Doing sit-ups
Muscle 1: Transversus abdominis
- Action: Compresses abdomen
- Innervation: Thoracic spinal nerves T8–T12, iliohypogastric nerve, and ilioinguinal nerve
Muscle 2: 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.
4. Breathing
Muscle 1: Diaphragm
- Action: Contraction of diapraghm 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 2: 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:
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy and physiology (15th ed.). Wiley.