How to do the plank correctly
FirstlyLooking from a distance, your upper body can seem to be parallel to the floor, but it is not what really makes the difference. The important thing is to engage the right muscles. Firstly, make sure you are not collapsing in the upper back. Broaden and depress your shoulders, and lift between the shoulder blades. Second, make sure you don't stick your tailbone up. In the plank position slightly tilt the pelvis: move the top of the hips sligthly up, the tailbone down. These will lengthen your spine and activate the right muscles around your shoulders and core. Make sure you can breathe smoothly and effortlessly into your stomachbelly.
How to make sure you're doing it right
The easiest is to have someone correct you, by touching the spots where you have problems, and gently adjusting you so that you get a feel for what the verbal instructions mean. If no-one is available, you can try to get the feeling in the following way:
- Put the knees down. This is important, even if you can do it with your knees lifted. Look in a mirror so that your upper body is parallel to the floor. Push the mat away with your forearms. Then, pull with the knees forward as if you'd want to pull your mat forward (nothing needs to move, just feel the forces). This will activate your core and straighten (or even flex slightly) the spine. Only when you are familiar with this, then lift your knees, but you need to maintain the same feeling around your core and shoulders.
How to progress
Once you can do 2-3 minutes, progress to more dynamic versions (eg. lifting one hand-leg, or doing it on unstable surfaces, balls etc. so you need to stabilize more). There's no need to do hours of it. If you can do a few minutes, move on to something more challenging.
Good luck!