The Manual of Gainful Exercise is a magical book that increases one reader's Strength. After use, the manual loses its magic but regains it in a century. The Mighty Nein acquired this book during a heist of the Tumblecarve residence in Uthodurn, the original intent being to retrieve a special ring for Ava Endlewood of the Plexis Post. While initially in Fjord's possession, he later gifted the book to Yasha Nydoorin upon her liberation from Obann. Over the next few days, she finally finished the book in The Xhorhaus prior to the initial attempt to restore Nott to her halfling form. Upon finishing it, her Strength increased from 17 to 19.
The book's magic is currently expended and recharging, and as of "High Seas, High Stakes" (2x99) it is still currently in Yasha's possession.