Your body should form a T or a cross. Brace your core—as if you were about to be punched in the gut—and maintain that contraction the entire time. Hold this position for the prescribed ...

At 5 months old, Liam Hoekstra of Grand Rapids, Mich., started doing an expert gymnast move called the iron cross. By 8 months old, Liam could do a pull-up and by 9 months, he could climb up and ...