smcj wrote:Start doing them before the retreat. On a physical level it is like getting into shape for any physical exercise. You do NOT want to just start doing hundreds a day! You will be so sore you'll have to stop, and your other meditations will suffer as well. Get into shape before the retreat!
The important thing about prostration boards (if your teacher will allow them) is that your feet are 3"-4" below where your knees hit. That makes pushing up MUCH easier, which saves your stomach muscles. Also get a soft pad and tape it down where your knees hit. A couple pieces of spare carpet will do for hand sliders. I use a swimmers lap counter instead of a hand male to count. It fits on your finger and isn't sliding around, which can be annoying.
There are the three main injuries that turn prostrations into a harmful and injurious activity as opposed to what they are supposed to be: a yoga for loosening the main channels of the body. These are: Injuries to the cervical spine, the lumbar spine, and the knees.
To prevent injuries to the neck, lower your head as you bend down.
To prevent injuries to the small of your back as well as your knees, you should never allow your knees to "hit", nor should you slide out from a kneeling position. You should slide out to the up position of a pushup, and then lower your body in such a way that you do not "hit" your knees (which causes many practitioners to have lifelong knee injuries) nor strain the small of your back.
When you rise, keep your head down while you slide back onto your knees, and then when you stand, keep your head down until you are full standing, rolling up from the base of the spine.
Despite the masochism with which many people approach prostrations, prostrations, and indeed no spiritual activity, should be a cause for harming the body, especially if you are a Vajrayāna practitioner, since knowingly harming the body is violation of root samayas.