After Butters Stotch eats an ounce of Chinese food from City Wok each day, he ends up gaining a lot of weight. Eric Cartman takes him to the Flex Gym Fitness Club to use the rowing machine so he can lose all the weight for the commercial later in the day, with Cartman offering him some of his "motivational help". However, he ends up still fat right before the commercial, so The Boys decide to perform liposuction on him.
The exterior of the gym is rectangular and has the "Flex Gym" part of its name written in white inside a red circle flexing its muscles. The rest of its name is written in red, including "24-hrs" written next to it. Its entrance doors have a small roof and two columns.
The interior of the gym has many workout machines, including the rowing machine that Butters uses. It has a dark blue, sky blue, and green colored floor and orange walls.