Double Duty: Strength-Training Moves That Get Your Heart Rate Soaring

Adding a new variation to basic plank is a great way to challenge your body's strength even further, and the plank jack is no exception. See how fast you can let yourself go while still keeping good form — your heart will thank you for it!

• Begin in plank position, with your shoulders over your wrists, your body in one straight line, and your feet together.
• Like the motion of a jumping jack, jump your legs wide and then back together. Jump as quickly as you want, but keep your pelvis steady and don't let your butt rise toward the ceiling.