Wherever there are feelings of ease or pleasure in the body, breathe in a way that protects them. Once you’ve got these feelings established, then allow them to spread through the body.

"The steps in this second tetrad are these: You train yourself to breathe in and out sensitive to rapture, to breathe in and out sensitive to pleasure, to breathe in and out sensitive to mental fabrication — which are your feelings and perceptions — and then to breathe in and out calming mental fabrication.

With regard to the first step, of inducing rapture, note that the word for rapture here, pīti, can also mean refreshment. In some instances and for some people, these sensations will be strong and clearly rapturous, even ecstatic. For others, they will be gentler and simply refreshing. This is not a measure of the power of your concentration. It’s simply an indicator of how much energy your body has been lacking, and how it responds when the energy becomes more full.

The Buddha says elsewhere that the kind of rapture you’re trying to induce here is both physical and mental. You induce physical rapture or fullness by the way you breathe; you induce mental rapture by the perceptions you cultivate.

For instance, if you breathe out in a way where you’re squeezing the energy out of the body, that’s not going to help with the physical sense of rapture. You have to breathe out in a way that doesn’t squeeze things. You can tell yourself, “I’ll put energy into breathing in. Let the body breathe out on its own. I don’t have to squeeze the breath out.” You also have to be careful not to squeeze anything at the end of the in-breath or the end of the out-breath. This, too, is a common mistake when people are doing breath meditation: They want to have a clear dividing line so that they can know, “This is the in-breath; this is the out-breath.” So they make a little squeeze between the two in the energy field of the body.

Learn how to resist that temptation. You don’t need that clear a dividing line. Think of the in-breath flowing into the out-breath, and the out-breath flowing into the in-breath: breath breathing breath. Don’t squeeze to make a distinction between the two. You’ll find that if you don’t squeeze the energy out as you breathe out, and you don’t make a little squeeze as you’re switching from one breath to the next, a sense of fullness begins to develop in the body. That, Ajaan Lee would identify with rapture. It’s a sense of refreshment, a sense of energy flowing around.

Then you can do the same thing with pleasure — sukha, which can also be translated as ease. Wherever there are feelings of ease or pleasure in the body, breathe in a way that protects them. Don’t squeeze them; don’t destroy them.

Once you’ve got these feelings established, then allow them to spread through the body, following your sense of the breath permeating the whole body."

~ Thanissaro Bhikkhu "Facing Aging, Illness, & Death: The Central Teaching of the Buddha"