The effect of the contraction of the muscles of the diaphram is that

The effect of the contraction of the muscles of the diaphragm is that the volume of the thoracic cavity increases. The diaphragm is a sheet of muscle that separates the chest cavity from the abdominal cavity. When the diaphragm contracts, it flattens out and moves downward, which increases the volume of the thoracic cavity. This, in turn, causes a decrease in pressure within the thoracic cavity, allowing air to flow into the lungs. As the volume of the thoracic cavity increases, the lungs are able to expand, drawing air in through the nose and mouth. The increased air intake brings in more oxygen, which is necessary for the body's metabolic processes. Therefore, the effect of the contraction of the muscles of the diaphragm is that the volume of the thoracic cavity increases, allowing air to flow into the lungs and providing the body with the necessary oxygen.