After losing his ability to walk to polio at the age of 39, Roosevelt took up swimming three times a week to strengthen the muscles in his arms, stomach, and lower back.
After a few months, Roosevelt was able to walk short distances with the help of a cane or assistance from an aide. After his election, the New York Daily News donated a pool to the White House so Roosevelt could continue the practice.
Source: Franklin D. Roosevelt Presidential Library, White House Historical Association