1. Turning a door knob
Brachialis
- Action: Flexes forearm at elbow joint
- Innervation: Musculocutaneous and radial nerves
Pronator teres
- Action: Pronates forearm at radioulnar joints and weakly flexes the forearm at elbow joint
- Innervation: Median nerve
Pronator quadratus
- Action: Pronates forearm at radioulnar joints
- Innervation: Median nerve
2. Throwing a baseball overhead
Latissimus dorsi
- Action: Extends, adducts, and medially rotates arm at shoulder joint; draws arm inferiorly
- and posteriorly
- Innervation: Thoracodorsal nerve
Deltoids
- Action: Lateral fibers abduct the arm at the shoulder joint; anterior fibers flex and medially rotate the arm at the shoulder joint; posterior fibers extend and laterally rotate the arm at the shoulder joint
- Innervation: Axillary nerve
Extensor carpi radialis longus
- Action: Extends and abducts hand at wrist joint (ulnar deviation)
- Innervation: Radial nerve
3. Kicking a ball
Gastrocnemius
- Action: Plantar flexes foot at the ankle joint and flexes leg at knee joint
- Innervation: Tibial nerve
Soleus
- Action: Plantar flexes foot at ankle joint
- Innervation: Tibial nerve
Psoas major
- Action: Psoas major and iliacus muscles acting together flex the thigh at the hip joint, rotate the thigh laterally, and flex the trunk on hip as in sitting up from a supine position
- Innervation: Lumbar spinal nerves L2-L3
4. Doing sit-ups
Rectus abdominis
- Action: Flexes vertebral column and compresses the abdomen
- Innervation: Thoracic spinal nerves T7-T12
Internal oblique
- Action: Acting together, compress the abdomen and flex the vertebral column; acting singly, laterally flex the vertebral column, especially the lumbar portion, and rotate the vertebral column
- Innervation: Thoracic spinal nerves T8–T12, the iliohypogastric nerve, and the ilioinguinal nerve
External oblique
- Action: Acting together (bilaterally), compress the 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
5. Walking
Soleus
- Action: Plantar flexes foot at ankle joint
- Innervation: Tibial nerve
Tibialis anterior
- Action: Dorsi flexes foot at the ankle joint and inverts (supinates) foot at intertarsal joints
- Innervation: Deep fibular (peroneal) nerve
Tibialis posterior
- Action: Plantar flexes foot at the ankle joint and inverts (supinates) foot at intertarsal joints
- Innervation: Tibial nerve
6. Breathing
External intercostal
- Action: Contraction elevates ribs and increases anteroposterior and lateral dimensions of the thoracic cavity which results in inhalation; relaxation depresses ribs and decreases anteroposterior and lateral dimensions of the thoracic cavity which results in exhalation
- Innervation: Thoracic spinal nerves T2–T12
Internal intercostal
- Action: Contraction draws adjacent ribs together to further decrease anteroposterior and lateral dimensions of the thoracic cavity during forced exhalation
- Innervation: Thoracic spinal nerves T2–T12
Diaphragm
- Action: Contraction of the diaphragm causes it to flatten and increases the vertical dimension of the thoracic cavity which results in inhalation; relaxation of diaphragm causes it to move superiorly and decreases vertical dimension of thoracic cavity which results in exhalation
- Innervation: Phrenic nerve, which contains axons from cervical spinal nerves (C3–C5)