Final answer:
During intense exercise, the metabolic activity of muscle increases the partial pressure gradient for carbon dioxide, facilitating its movement out of the tissue.
Step-by-step explanation:
During intense exercise, the metabolic activity of muscle increases the partial pressure gradient for carbon dioxide, facilitating its movement out of the tissue. Cellular respiration continuously produces carbon dioxide, causing it to diffuse out of the tissue and enter the blood. This is due to the lower partial pressure of carbon dioxide in the blood compared to the tissue.