Pain For Pleasure
Algolagnia, from the Greek, is the psychological term to describe Love of pain, or "pain given in love"...
The Endorphin-kick
During sadomasochism activities the human body makes endorphins, or more exact Beta-endorphins, a chemical produced naturally by the body. Endorphins are neurotransmitters, chemicals which are directly involved in the brain's electrochemical workings and involved in regulating the perception of pain. The name is derived from "endo-" meaning internal, and the name of the drug morphine — endorphins are chemically similar to opiates. The detached euphoria is what is sought after by the submissive/slave/boy and enjoyed as a result of pain derive from the release of these endorphins.
The methodical application of pain can move the pain threshold higher, enabling the submissive/slave/boy to tolerate higher levels of pain, thereby receiving the benefits of higher endorphin levels which leads to the submissive/slave/boys pleasure. The pain will not always seem to increase, even though the physical trauma upon the body does. This is because as endorphin levels rise, the pain becomes deadened.
In order to stimulate the release of endorphins, the experienced Master will gradually increase the pain level/intensity until it nears the submissive/slave/boys pain threshold. After reaching the threshold, the experienced Master will lower the intensity and allow the endorphins which the pain released to work their magic, nullifying the pain. When the Master once again begins to increase the pain, the endorphins which the previous cycle released allow the submissive/slave/boy to tolerate a higher level of pain. The now higher level of pain releases even more endorphins, and the cycle begins again until the submissive/slave/boy finds utopia.
Sometimes the pain threshold will hit a plateau, refusing to rise further. If this happens, a complete break in activity for a few moments, a few minutes or longer is in order. Every submissive/slave/boy has a certain point beyond which even the best technique cannot take them. This point can vary from day to day.
Some people use poppers, the common name for amyl (or alkyl, butyl or propyl) nitrite, also known as aromas. These are volatile compounds whose vapors cause temporarily increased heart and breathing rates, muscle relaxation and a characteristic "rushing" feeling in the head and are often used as disinhibitor, muscle relaxant and means of raising the pain threshold. There are dangers associated with their use. It should be noted that we do not endorse the use of aromas. However, there are those that do use, or require the use of aromas or enhancements, so you should be aware of them.
Pleasure And Its Relationship With Pain
There are two very different aspects to the relationship between pleasure and pain; one of them is mental and the other is physical. This is why we can easily notice the extreme difference between the people that like to bottom (pure masochists) and submissive/slave/boys who can delve in pain only as long as it comes from somebody they are deeply involved with emotionally. (the typical "I don't like that, but I'll do it for you")
This difference, then, comes from the mental/physical duality of the relationship between pleasure and pain, and from the ability of the brain to transform what we feel into anything it wants to transform it to, so long as it wants it hard/bad enough. This ability can be nurtured by a Master if he knows and understands how the brain works. This is a big part of what many of us define as "training the submissive/slave/boy".
What Our Nerves Call Pleasure And Pain
Our skin is covered with nerve endings that transmit information to the brain; this starts with the contact of our nerves with the environment and creates electrical impulses that then travel through the nervous system to our brain. Now, these electrical impulses are, for obvious reasons, very lightly charged, which means that the information they can carry is limited, and it's up to the brain to interpret what it means and how to react to the stimuli. As it happens, the nerves that sense pleasure and the nerves that sense pain are the same, and the signals they send when feeling one or the other are very similar, the difference being the intensity of the signal. That's one of the reasons why a slow change in temperature is felt much less than a fast change. As it is proven every time you work around the kitchen, if the temperature increase is slow enough, your nerves can be fooled into never raising the alarm.
The difference between pleasure and pain then is the intensity of the electrical signal sent by the nerves to the brain. The nerves can be fooled into not raising the "pain!" alarm if the circumstances are appropriate...and if we manipulate the circumstances so they become appropriate, we can manage to fool the nervous system...and make it recognize pain as pleasure (and even pleasure as pain, if we wish to do that). An easy way to recognize this phenomena is to watch your submissive/significant other when having sex with him...if you stimulate his cock long enough, he'll cum...but if you keep stimulating it, at some point in time (for some sooner and for others later), he'll feel pain instead of pleasure (strange but true).
Another important physical factor in the pleasure/pain equation is the protein called endorphin (discussed somewhat above) that ends up putting the submissive/slave/boy in subspace. This protein is defined as "any of a group of opiate proteins with pain-relieving properties that are found naturally in the brain. The main substances identified as endorphins include the enkephalins, beta-endorphin, and dynorphin, which were discovered in the 1970s by Roger Guillemin and other researchers. Endorphins are distributed in characteristic patterns throughout the nervous system, with beta-endorphin found almost entirely in the pituitary gland" according to the Encyclopedia Britannica.
These proteins get released into the bloodstream under several circumstances (I actually found an article that talks about runners getting "addicted" to endorphins released during long jogging sessions) and BDSM activities seem to be among them. On the part of the Master it seems easy to understand, since he's the one that generally does the most exercise during a scene, but it is actually in the submissive/slave/boy where we see the effects of this opiate-like group of proteins the most. The brain seems to release endorphins (especially beta-endorphins) during a scene when the pain is increased in a slow and steady way, and we notice it in the submissive/slave/boy by several signs. First of all, his reactions seem to be slower than usual, his speech blurs a bit and his reaction to whatever toy we are using on him is less than it was when we started. This ends up with the submissive/slave/boy going into what we call "subspace" or utopia state...which can be, in many ways, defined as an endorphin high or endorphin-kick.
Once we realize that pleasure and pain are tightly intertwined in the brain, we can start to think about ways to modify the response to those stimuli, making the pain threshold move higher, so the pleasure threshold is bigger. Each submissive/slave/boy will react differently to this, and the results vary wildly...but it can be done, with enough patience and practice.
What Your Mind Calls Pleasure And Pain
OK, so the body can be fooled into turning pain into pleasure and vice-versa...but that will only take you so far. The mind, as we said, has a lot to do with this also, and proper training can help us push the envelope of this even more. A "painslut" is not just somebody whose body has been fooled so often that it thinks it's the way it is...his mind has to be tuned into the scene also, which will help us when we try to bring him into subspace.
I think all experienced Masters will agree that a submissive, even a "painslut", is not always ready for the same amount of pain. The main (but not the only) reason for this difference between scenes is the mind. The degree of participation and preparation of the mind for the scene has a lot to do with the level of pain he will be able to turn into pleasure. Recognizing this is important, both for the fun of the scene and, the most important, for the well being of the submissive/slave/boy.
The mind has to be tuned into the scene as slowly and carefully as the body, otherwise the reactions of the submissive/slave/boy will not be the ones the Master expects. The real deal here is, that if the mind isn't cooperating with the scene, the brain will not release the endorphins necessary for the submissive/slave/boy to be able to take the amount of pain the Master is delivering. As I've said, if the body and mind don't work together, the brain will not be able to process the pain as a form or pleasure.
There are several different approaches to getting the brain involved in the scene, from ritualistic to circumstantial (who hasn't felt the perfect click when scheming, coming from something we can't even vocalize?) and we have to learn how to recognize this and be prepared to use it in our favor.
Also, as part of the mind participation, comes the submissive/slave/boy's expectations and experiences. If a submissive/slave/boy has had a bad time with, for example, a paddle, he will have a hard time turning a paddling into a pleasurable experience. Knowing and understanding these "mental scars" is of extreme importance in the Master's journey with his submissive/slave/boy...when the Master ignores this, he is setting himself up for a very ugly time/scene. That is one of the many reasons that it is so very important for the Master to always talk with his submissive/slave/boy/masochist, whatever, before introducing anything new in a scene, so both know what they are getting into and both will enjoy the benefit of the scene.
Well, now that you sort of have the basics of how pleasure and pain are dealt with by the body and the mind, you can start thinking about *how* to use this so that you can start expanding your limits of enjoyment.

Take a risk. Play. Explore. Learn. Enjoy!