Final answer:
During normal exhalation, the internal intercostal and abdominal muscles contract.
Step-by-step explanation:
During normal exhalation, the muscles that contract include the internal intercostals and abdominal muscles.
The internal intercostals muscles aid in drawing the ribs together to constrict the rib cage, while the abdominal muscles assist in increasing the force of exhalation by compressing the abdominal organs and pushing the diaphragm up into the thoracic cavity.