In 2004, a German toddler shocked neurologists at Berlin's Charité hospital. At four and a half years old, the boy could hold seven-pound dumbbells with his arms extended. His quads bulged like tree trunks. He was roughly twice as strong as other kids his age.

This wasn't some toddler CrossFit cult, nor was he dosed with steroids. He'd been born with a genetic mutation that shut off his body's production of myostatin, a protein that inhibits muscle growth (it literally means "muscle remain").

His mother, a former sprinter, carried one copy of the mutation, and several of his relatives were known for their unusual strength, including a construction worker who could unload heavy curbstones by hand. Like Belgian Blue cattle and "Mighty Mice" before them (cattle and mice breeds genetically engineered to be freakishly muscular), this toddler's family was naturally hypertrophic.