I. throwing a baseball overhead
- 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.
2. Supraspinatus
- Action: Assists deltoid muscle in abducting arm at shoulder joint.
- Innervation: Suprascapular nerve
II. kicking a ball
- Gastrocnemius
- Action: Plantar flexes foot at ankle joint and flexes leg at knee joint.
- Innervation: Tibial nerve
2. Tibialis anterior
- Action: Dorsiflexes foot at ankle joint and inverts (supinates) foot at intertarsal joints.
- Innervation: Deep fibular (peroneal) nerve.
III. 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.
2. Transversus abdominis
- Action: Compresses abdomen.
- Innervation: Thoracic spinal nerves T8–T12, iliohypogastric nerve, and ilioinguinal nerve.
IV. Breathing
- 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.
2. 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).