'Up until about the mid 1940’s, many boxers wrestled in training camp as part of their strength-and-conditioning program. It was a common practice. A few examples:
Last Bare-Knuckle champ John L. Sullivan trained under William Muldoon, top pro wrestler, physical culturist, and later chairman of the New York State Athletic Commission. Forgotten Heavyweight Champ Jim Jeffries also wrestled in training camp, and his wrestling skills were respected by top grapplers. Will-O-The-Wisp Willie Pep trained in wrestling specifically for the Sandy Saddler fight. While looking through old boxing photos, I’ve seen photos of old-time boxers on the mat grappling.
Legendary Heavyweight Champion of the 1920’s, “The Manassa Mauler” Jack Dempsey, also wrestled in training camp and later took judo lessons. '