1. Stand strong, with your feet placed at about shoulder width apart, a slight bend at the knee, with your hands by your sides
2. Lightly, but explosively jump off the balls of your feet out to the side away from each other while simultaneously bringing your hands up into the air to meet above your head
3. Again, use the balls of your feet to lightly jump your feet back into the starting position, while lowering your hands back down to your sides
The primary muscles used in Star Jumps/Jumping Jacks are the Abs and Calves. The secondary muscles used are the Shoulders.