Well, the thing is that doing a plank is really helpful for your total body.
A lot of muscle groups are forced to work simultaneously while doing a plank. And that is why holding a plank generates more muscle than a single ab crunch or a tricep curl.
So, which muscle groups a plank really forces to work?
As far as your midsection is concerned, the lower back, the inner, outer and oblique abdominals strain to keep your body in a straight position without letting your hips droop.
Your lower body also participates with your glute muscles, quadriceps (thighs) and calfs.
So, planks help you strengthen your whole body.
They also help you become more flexible, as they stretch your shoulder blades, hamstrings, feet and lengthen your legs and of course your total body.
As your body stretches and becomes flexible, you are also likely to maintain a better posture.
Of course, a plank exercise challenges you mentally. That is, because you're trying to maintain the plank position for as long as you can handle. With a little bit more of mental effort, you can push yourself to keep the plank position longer, even if you feel like your whole body is burning like crazy.
The basic plank exercises are the following:
-front plank
-side plank