The plank exercise is one of the most effective out there because it strengthens both the shoulders and the abdominal region, as well as the legs.

Planks are also useful for helping burn off stubborn belly fat. Planking builds your core muscles, and muscles burn even more calories. This extra burn makes it easier to lose weight.

Planking is also wonderful because it is low impact. You're very unlikely to hurt yourself and you won't end up straining any of your muscles, joints, or ligaments.

But four minutes of planking must be pretty hard, right? Well, the fortunate thing is that we build our way up to it. The plank challenge adds just a few seconds most days.

You start at 20 seconds a day, move up to 30, 40, then 45 and so on. This allows your body to get used to the exercise and helps you get better at it. The longer you can hold it, the better off you are.

The challenge: