According to The New York Daily News, the visual evidence that led Yankee teammates to suspect A-Rod was still using PED's were his large breasts, aka "man boobs". Males develop large breasts as a result of steroid use when the body increases production of female hormones to offset the increase in testosterone. This medical condition is called gynecomastia.
A-Rod was not the only Yankee great who suffered from the condition. Roger Clemens did also. The Daily News investigative team writing a book on Clemens, American Icon: The Fall of Roger Clemens and the Rise of Steroids in America's Pastime, write that Clemens must have been embarrassed by his condition based on his grooming patterns.
Roger Clemens had man boobs, and he must have been embarrassed because he was often the first Yankee out of the shower and the first to get dressed after the game.The article points to A-Rod's visual evidence when he went to the park as the shirtless park tanner that the general public picked up on. If this condition is prevalent in the locker room than perhaps George Costanza's father was on to something when he was designing the "bro" and the "manissiere".