The diaphragm links the respiratory to the muscular system by

Respiration

Explanation:

Respiration is the process of inhaling and exhaling. The muscles of respiration make up the muscular system which are responsible for inhalation and exhalation as well as the contraction and expansion of the thoracic cavity. The muscular system aids in pushing air into and also out of the respiratory system when the diaphragm contracts and relaxes respectively. The respiratory system delivers air to the muscles through the lungs.