A jumping jack is an exercise where you start standing with your feet together and arms at your sides, then jump while spreading your legs apart and raising your arms overhead, then jump back to the starting position. The movement looks a bit like making a snow angel while standing up.

Physical education teachers love jumping jacks because they warm up your whole body quickly. You might do twenty jumping jacks before playing kickball or running laps. Coaches use them for conditioning because they get your heart pumping and work your arms and legs at the same time.

Military training often includes jumping jacks as part of basic fitness routines, and they've been a staple of gym classes for generations. Some people call them star jumps because your body forms a star shape when your arms and legs are spread wide. They're simple enough that almost anyone can do them, yet challenging enough that doing fifty in a row can leave you breathing hard and feeling the burn in your muscles.