The following quote is from a Chan dharma talk by venerable Master Hsuan Hua:
"Chan investigation requires single-minded concentration. When single-minded concentration reaches its ultimate point, then you will be able to deal with things. It's said, "When things reach their extreme, a change must take place." It doesn't matter what the situation, by pursuing it to it's end, you can deal with it. Now as you sit in meditation, don't cry as soon as your legs start to hurt. After the pain reaches an extreme, it will stop and you will experience an inconceivable and ineffably wonderful state.
There is no way I can express that state to you; you have to experiment for yourself. Once you experience pain to the extreme point, you won't have any more pain. You will have broken through the pain barrier. But breaking through one barrier is not enough. After a while there will be another barrier, and then later on another barrier. The first pain barrier was after one hour.
But when you have sat for one and a half hours, the pain comes up again. Why does that happen? Your blood and qi (energy) reach a certain place, and they want to get through a barrier--another barrier of pain. And so you have to endure the pain again. You endure it until it doesn't hurt any more. Once the pain disappears, you will feel at ease and very happy--an inexpressible bliss, an ineffable comfort. At that time you will feel Earth over Heaven making Peace.
You must break through these barriers in order to attain benefits. If you act like a child who cries at the first sign of pain, then you will never be able to break through these barriers. You need to have patience. Endure what is unendurable! Grit your teeth and bear it! But you must be resolute! Don't fear suffering! Don't fear pain! Don't fear difficulty! With these three kinds of fearlessness, you can break through the three barriers." (source: http://www.cttbusa.org/dharmatalks/chan2.asp
Do you know if this is specific to chan meditation practice or if it is the same way with other types of sitting meditation practice?
I also wonder about the timing - in the quoted text Master Hsuan Hua says that the first barrier is reached after one hour, but I have managed to sit in half lotus for maybe 70 minutes, and regular cross-legged for 90 minutes, without reaching a barrier, after maybe 50 minutes my body starts shaking and I start cold sweating, but the pain in the legs just gets worse and worse without any sign of reaching a maximum, and after a while I can't take it and gives up. I read somewhere that one chinese hour equals two western hours - maybe Master Hua was refering to one of those hours?
Do you know how much time it is supposed to take to reach the first pain barrier? And do you know if the posture is important? Is it only with full lotus, for instance, that it happens as Master Hsuan Hua says, or does the same thing happen with half lotus and regular cross-legged pose?
What are your experience with the pain barriers? Have you broken through them? How long did it take? Do you have to break through each of them every time you sit, or is each particular pain barrier done with once and for all when you have been able to sit through it?
I also read somewhere that the hell realms corresponds with our legs, and that by sitting through the pain barriers one liberates the tormented beings that resides there. Do you know anything about this?