The gym shoe is a Chicago sandwich that works by colliding three of the city's other sandwiches into one roll. Italian beef, corned beef, and gyro meat are piled together under melted mozzarella, dressed, and the point is the collision: the wet, jus-soaked beef, the cured and spiced corned beef, and the seasoned spit-roasted gyro lamb-and-beef are each a Chicago tradition in its own right, and the gym shoe argues they belong in the same bite. The defining engineering is not any one meat. It is a roll asked to carry three heavy, differently wet fillings at once without folding.
The craft is in load management on a structural roll. Italian beef brings jus and the constant threat of a soaked, collapsing crumb; corned beef brings fat and salt; gyro meat brings grease and its own moisture. Stacked together that is more wet weight than any single Chicago build puts on a roll, so the bread has to start with a crust sturdy enough to absorb the jus and still lift, the same engineering the Italian beef demands, pushed harder. The mozzarella is added over the hot pile so it melts down through the meats and binds them into one mass rather than three sliding layers, which is the difference between a designed sandwich and a fistful of deli scraps. It is dressed and often finished with giardiniera, whose oil and pickled bite supply the acid and crunch that cut three rich proteins at once. This is a fast-food and corner-stand build in Chicago, the meats held hot and separate on the line and combined to order, because each one is also sold as its own sandwich.
The variations are mostly which meats and how wet. A version dipped harder toward the Italian beef end, a build that swaps the corned beef or adds a sausage, a drier assembly that leans on the gyro. The wider long-roll shelf, the Italian beef itself, the hero, the chain submarines, runs the same load-bearing-roll logic with single fillings. Those deserve their own articles rather than being crowded in here.