A plank is a simple total-body exercise that strengthens and tones your core muscles, your arms, thighs and calves. It’s a great full-body workout that you can do in under a minute to improve your health and fitness. As you build strength in your core, you can add variations to the planking exercise to isolate particular muscle groups in your body. It is best to begin with doing a basic plank and building up your endurance. Take the plank challenge for the next 28 days to get started.