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: Subscapularis
Action: Medially rotates arm at shoulder joint.
Innervation: Upper and lower subscapular nerve
2. Kicking a ball
Muscle: Rectus femoris
Action: extend leg at knee joint; flexes thigh at hip joint
Innervation: femoral nerve
Muscle: Sartorius
Action: weakly flexes leg at knee joint
Innervation: femoral nerve
3. Doing sit-ups
Muscle: Rectus abdominis
Action: Flexes vertebral column, especially lumbar portion, and compresses abdomen
Innervation: Thoracic spinal nerves T7-T12
Muscle: Transverse abdominis
Action: compresses abdomen
Innervation: Thoracic spinal nerves T8-T12, iliohypogastric nerve, and ilioinguinal 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