Exercise improves tumor blood vessel quality and density, which enhances chemotherapy drug delivery to the tumor.

“exercise combined with chemotherapy is more effective than exercise alone or chemotherapy alone and what they've shown in these studies is um that these primary tumors have a very poor vasculature it's poor quality blood vessels they're leaky uh and they're chaotic in there but all these tumors in order to grow they need to draw blood vessels they only grow to a very small size and unless they get blood vessels within them they can't grow any larger so they all start developing these blood vessels what they were able to show uh in these uh exercise studies that excise improves the quality of these blood vessels and the density of these blood vessels”