Good feelings lead to addiction
Cracking a joint is usually rather enjoyable and makes you feel better.
Maybe a "pop" activates some bodily reactions which you can get addicted to.
At http://en.wikipedia.org/wiki/Cracking_knuckles a chiropractic gave some insight on what happens when a joint cracks:
[…] The sudden j**k on the capsule and the other periarticular tissues is theorized to cause firing of the high-threshold mechanoreceptors. […]
We should look into what firing of these mechanoreceptors does.
Yes, it relaxes the muscle and stimulates the nerve endings. :lol:
Well, I just took a little closer look into the mechanoreceptor theory. This is what I found. As usual bold is by me.
There are Type III mechanoreceptors in the capsular-ligament complex of a synovial joint. They are similar in strucutre to Golgi tendon complex (GTOs) that when activated, will create a reflexive inhibitory effect on the joint capsule and surrounding musculature.
During Grade V joint manipulation, the manipulator is reaching the end-range of the tissue and is changing the pressure inside the capsule. Nitrogen changes from a liquid to a gas state within the synovial joint that expands the limits of the capular ligaments. This activates the Type III mechanoreceptors and creates relaxation. The audible sound of "cracking a joint" is the sound of nitrogen turning from a liquid to gas state.
An analogy is when you open a champange bottle. While taking off the cork, you hear a pop and forceful pressue pushing the cork out of the bottle. You have changed the pressure within the bottle and creating a change from liquid to gas.
Here is a well done highly scientific review of papers done by Dr. Donald Murphy in 1996:
MECHANISMS INVOLVED IN JOINT MANIPULATION
1. Suter E, Herzog W, Conway PJ, Zhang YT. Reflex response associated with manipulative treatment of the thoracic spine. J Neuromusculoskel Sys 1994; 2(3):124-130.
2. Gail JM, Herzog W, et al. Forces and relative vertebral movements during SMT to embalmed post-rigor human cadavers: Peculiarities associated with joint cavitation. J Manipulative Physiol Ther 1995; 18(1):4-9.
3. Reggars JW, Pollard HP. Analysis of zygapophyseal joint cracking during chiropractic manipulation. J Manipulative Physiol Ther 1995; 18(2):65-71.
4. Brodeur R. The audible release associated with joint manipulation. J Manipulative Physiol Ther 1995; 18(3):155-164.
5. Herzog W, Conway PJ, Zhang YZ, Gal J, Guimaraes ACS. Reflex responses associated with manipulative treatments on the thoracic spine: a pilot study. J Manipulative Physiol Ther 1995; 18(4):233-236.
6. Herzog W. Mechanical and physiological responses to spinal manipulative treatments. J Neuromusculoskel Sys 1995; 3(1):1-9.
The mechanisms involved in joint manipulation are of obvious interest to chiropractors in attempting to better understand what it is that we do. Oftentimes that manipulative or adjustive procedures that we utilize are associate with phenomena such as the audible release. The exact physiological events that occur when a patient is adjusted have been the topic of some intense and fascinating research in the recent chiropractic literature. As can be seen, much of this work arises from Dr. Herzog's laboratory at the University of Calgary.
The first study looked at the immediate reflex responses of manipulations to the thoracic spine. The investigators measured surface EMG responses in paraspinal and more lateral (serratus posterior inferior) muscles after fast manipulations and slow manipulations and also measured the differences in responses between those in which cavitation took place and those in which it did not. They found that a brief increase in EMG activity was seen after fast manipulations regardless whether cavitation took place or not. A much smaller response was seen after slow manipulations, and again there was no difference in response between those with cavitation and those without. Responses were seen not only in the muscles at the same level as the adjustment but at other levels as well as in the more peripheral muscle measured. The response to fast manipulation was a quick burst of activity while that to slow developed more slowly.
It is interesting the difference in response related only to whether the manipulation was fast or slow, not to whether cavitation took place. In other words, an audible release was not necessary for the burst of muscle activity to be stimulated, but the adjustment did have to be fast to produce this response. It is important to remember that these findings relate to immediate responses, not those measured a period of time after the treatment.
Study number 2 represents the first experiment of manipulation on a cadaver. An examiner manipulated the T12 segment 5 times, achieving cavitation once, on the fourth trial. The only recorded difference between the manipulations was that there was a greater lateral translation of the vertebra against the adjacent vertebrae on the manipulation with cavitation. So when an audible release took place, there was a greater amount of movement created by the adjustment. This shows a distinct difference between cavitation and non-cavitation, but does not illuminate if this has any therapeutic import.
The third study looked at 51 asymptomatic subjects who were manipulated at C3-4 with a rotatory diversified adjustment. In most cases, there were 2-3 audible releases and in 94% of the cases the release was on the side to which the head was turned, not the contact side. In the three in the whom the crack was on the contact side, all had previous trauma. This is interesting because we often assume that the joint that we are contacting is the one that were are adjusting, but this study shows that this may not be the case. As the subjects in this study were asymptomatic, and there apparently was no attempt to determine whether the joint adjusted was determined to require an adjustment, we cannot necessarily associate this with a true clinical situation. This needs to be reproduced in a symptomatic population before firm conclusions can be drawn.
The fourth paper is a review of the literature on joint cavitation which revealed some new and interesting findings from recent research. It is explained that as a joint is being distracted, the capsule invaginates inward and as the stress on the capsule reaches a certain threshold, it suddenly snaps back from the synovial fluid, increasing the volume of the capsule (and decreasing pressure) and causing the audible sound. The sudden increase in the volume causes the tension to drop, allowing the joint to increase in movement. Eventually, the elastic limit of the capsule is reached and the process stops. The time elapsed during all this is shorter than that required for completion of the stretch reflex, so it can occur without muscular resistance. The sudden j**k on the capsule and the other periarticular tissues is theorized to cause firing of the high-threshold mechanoreceptors. This is an interesting update on our understanding of this phenomenon, and the paper includes some effective diagrams and load-separation curves to illustrate the current knowledge in this area.
This paper also discusses the commonly held belief in some circles that repeated knuckle cracking leads to the development of DJD. There is inconclusive evidence to determine whether this is true, but one study showed increased incidence of swelling of periarticular tissues and decreased grip strength among habitual knuckle crackers.
Paper number 5 reports on a study that is actually a pilot study to study number 1 reviewed here, although this pilot was published shortly after the main study. As with the other study, it showed that fast manipulations produced a burst of activity in muscles directly adjacent to the level manipulated and that slow manipulations did not. Also, this response was independent of the presence of an audible release. Some of the fast manipulations did not produce a release and some of the slow manipulations did, but still, all of the fast manipulations produced a response and none of the slow ones did.
The final paper by Dr. Herzog reviews the literature on his and other studies on the immediate responses that have been measured resulting from manipulation. It is an interesting review of all of this research and helps shed light on the physiological phenomena that are presently known to associated with spinal adjustments.
As we further investigate the exact events that are occurring during our treatments, we present ourselves with the opportunity to improve our methods and thus improve patient care. This should be the primary purpose of all research and all appraisal of research by chiropractic practitioners.
Chiropractors certainly have interesting insights in this topic. Tough food to swallow though.
Why do joint crackers feel the tension more strongly than others? It is quite obvious that releasing a tension feels good. :roll:
One more to add in favor of the addiction theory:
David Clarke started a thread worrying about his frequent cracking:
The following is for my own interest. I frequently "crack" my knuckles,
knees, ankles, elbows, etc. The "school-yard" explanation that I've
heard is that I'm releasing nitrogen gas from the blood. Any truth to
that? Does anyone know the mechanism behind this?
Incidently, I find that if I don't "crack" my knees frequently (4 or more
times per hour), then I find flexion/extension to be a very odd
sensation. Not painful, just a little stiff.
Can I develop arthritus year from now because I continue to do this to my
body? I've heard both yes and no.
Any insight would be appreciated.
He was referred to this paper:
1. Brodeur R.
The audible release associated with joint manipulation.
Jmpt (Journal of Manipulative & Physiological Therapeutics).
18(3):155-64, 1995 Mar-Apr. (40 ref)
Partap S. Khalsa had this to say:
The phenomenon you describe has been of considerable interest to the chiropractic, osteopathic, and physical medicine professions. In
particular, what is the cause of the "cracking" sound that commonly is
produced during spinal manipulations/adjustments. Please see the
following discussion written by R. Brodeur of the Dept. of Biomechanics,
Michican State Univ.
and quoted the referred paper:
OBJECTIVE: The objective of this paper is to review the literature on the audible release associated with manipulation.
DATA SOURCES: Bibliographic information in pertinent articles and papers
located in the MEDLINE database containing the
keywords: joint, joints, cartilage, crack, cracking, cavitation,
crepitus and noise.
STUDY SELECTION: All articles relevant to the objectives were selected.
DATA EXTRACTION: All available data was used.
DATA SYNTHESIS: The audible release is caused by a cavitation process
whereby a sudden decrease in intracapsular pressure causes dissolved
gasses in the synovial fluid to be released into the joint cavity. Once
a joint undergoes cavitation, the force-displacement curve changes and
the range of motion of the joint increases. The gasses released from the
synovial fluid make up about 15% of the joint volume and consist of
approximately 80% carbon dioxide. Habitual joint cracking does not
correlate with arthritic changes, but does correlate with loss of grip
strength and soft-tissue swelling. During the "crack" associated with a
joint manipulation, there is a sudden joint distraction that occurs in
less time than that required to complete the stretch reflexes of
periarticular muscles. Theories on the cavitation mechanism were
reviewed and new information on the cavitation process is introduced. In
this paper, it is proposed that the cavitation process is generated by
an elastic recoil of the synovial capsule as it "snaps back" from the
capsule/synovial fluid interface.
CONCLUSIONS: Because the sudden joint distraction during a manipulation
occurs in a shorter time period than that required to complete the
stretch reflexes of the periarticular muscles, there is likely to be a
high impulse acting on the ligaments and muscles associated with the
joint. This is an important conclusion, because others have proposed
that reflex actions from high threshold periarticular receptors are
associated with the many beneficial results of manipulation. This
suggests that the cavitation process
provides a simple means for initiating the reflex actions and that
without the cavitation process, it would be difficult to generate the
forces in the appropriate tissue without causing muscular damage.
David followed this up with a summary. He found two more interesting papers:
 Castellanos J., Axelrod D., "Effect of habitual knuckle cracking on
hand function". Ann Rheum Dis 1990; 49:308-309.
 Unsworth, Dowson, & Wright, 1971, "Cracking Joints: A Bioengineering
Study of Cavitation in the Metacarpophalangeal Joint," Ann. Rheum.
His conclusion is in favor of the addiction theory:
One response stated that the cracking of a joint can cause short term
relief, but that after a short while (hours, days, weeks), the previous
symptoms reappear. This can lead to an "addiction" of joint cracking and
is probably the reason why I crack my knees and fingers so much.
Once again it becomes obvious that we should look for and hunt scientific papers on this topic. The herin quoted papers are almost 10 years old so we can expect new results in new papers.
It is not hrad to understand that a nice feeling leads to addiction.
The brain if it keeps getting a good feeling will then make you go back to that place to get the same feeling. It has been scientifically proven. So, if you joint crack, you will want to joint crack to get that same feeling of satisfaction.
yup i think i saw in antoher thread that it releases endorphins too which is good i guess…
that is the good feeling.
cool, i guess it's easier than exercise to click your toe! (exercise releases endorphins too)
yeh i know - thats why some people do it a lot.
i should savour it when it happens then i guess, i usually get a bit worked up when they click.. cool
Yes but it won't last long.
Yes, it relaxes the muscle and stimulates the nerve endings. :lol:
then its a good thing!
Being burnt stimulates nerve endings.
No as in like putting your hand on a hot radiator etc