A British gym is trying to add human interest to otherwise dreary workouts by replacing traditional dumbbell weights with human ones.

The Gymbox chain gym in central London says fitness enthusiasts can now swap their usual lumps of metal for human beings in a range of shapes and sizes.

According to the gym's owner Richard Hilton, it's all about visualizing strength.

"Creating a mental image or intention of what you want to happen or feel is proven to improve physical and psychological performance," he said in a statement. "The human weight lifting apparatus ... is the ultimate embodiment of visualization theory.

The human weights range from the "Dainty Dwarf" 32-year-old Arti Shah, who weighs just 66 pounds up to the "Super Human" weight of 37-year-old — and 342 pound — Matt Barnard.