An Olympic gold medal-winning swimmer and world record holder has revealed that praying the Hail Mary calms her down before she competes in a race.

Four years ago in London, at age of 15, US swimmer Katie Ledecky won Olympic gold in the women's 800-metre freestyle.

Since then Ledecky, who attended Catholic schools in Bethesda, Maryland, has become the world record holder in the 400-, 800- and 1500-metre freestyles, and the American record holder in the 500-, 1000- and 1650-yard freestyles.

In the Olympics in Rio de Janeiro, she will compete in the 200-, 400-, and 800-metre freestyle.