Capillaries<span> are the smallest of the body's blood </span>vessels<span>. They are only one cell thick, and they are the sites of the transfer of oxygen and other nutrients from the bloodstream to other tissues in the body; they also collect carbon dioxide waste materials and fluids for return to the veins.</span>
Injury Prevention, sorry I just saw this question.
Both of Michael Phelps and Caleb Dressel are professional swimmers ( freestyle swimming) so D
