1. Throwing a baseball overhead
- Muscle: Latissimus dorsi
- Action: extends, adducts, and medially rotates arm at shoulder joint; draws arm inferiorly and posteriorly. RMA: Elevates vertebral column and torso
- Innervation: thoracodorsal nerve
- 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
2. Kicking a ball
- Muscle: Quadriceps femoris
- Action: extend leg at knee joint; rectus femoris muscle acting alone also flexes thigh at
hip joint.
- Innervation: femoral nerve
- Muscle: 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: 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
- 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: 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