In late 1939, after Paige had recovered from the severe arm injury that jeopardized his career, he re-designed his pitching repertoire to take better care of his arm. He still had an exceptional fastball but he did away with his fast curve, deciding to only throw slow curves from that point forward. He learned to throw a knuckleball from Cool Papa Bell, a pitch which he reportedly perfected in regards to its movement but did not always exhibit full control of. He also added a "slow sinker" and used his hesitation pitch more frequently. Along with these additions to his repertoire, Paige made greater use of his sidearm and submarine releases, which both made him a more deceptive pitcher and lessened the strain on his pitching arm.