Have you ever wondered what it is that NBA trainer to the stars Drew Hanlen does to boost the games of players like star Boston Celtics forward Jayson Tatum? The Pure Sweat head honcho recently took some time on a recent episode of the NBC Sports Boston's "Hoopin'" show to talk it over with NBC Sports host Kayla Burton.

Hanlen helped Tatum become the player he is today, and continues to help the Celtics star hone his craft to new heights. And now, Hanlen has a book.

“And he couldn’t even zip it up,” Drew Hanlen said. “He was at probably 320 pounds.”