Like acupuncture, acupressure was developed in China over 5,000 years ago, and is considered to be a complementary technique, as opposed to a "watered down" or "less effective" version of acupuncture. The two techniques use the same stimulation points and meridians, but while acupuncture uses needles, acupressure employs gentle but firm pressure to stimulate chi flow, and also integrates bodywork therapies, therapeutic touch, somatic work, healing imagery, energy psychology, and massage therapy techniques. Acupressure devotees claim that constant pressure is more effective than needle punctures at initiating the flow of chi, patients are generally more receptive to pressure than being punctured, and the opportunity to integrate other healing modalities simultaneously make it a more widely applicable technique.
Interestingly, the efficacy of acupressure has not been substantiated by rigorous clinical trials such as that described above for acupuncture. The reasons for this are open to rationalization, but no consensus currently exists. That millions of people get excellent, lasting relief via acupressure cannot be argued, however.
As can be appreciated by the admittedly small diagram of the hand to the left (maps of the entire body can be obtained as well, just as for acupuncture), the tolerances for acupressure are also very stringent. Often, when considering acupressure on the hand or foot, the organ can be seen as almost a miniature map of the human body. Looking at the hand, the eye is above all else, the liver is on the right (patient's perspective, as usual), adjacent to the yellow stomach and pink spleen; the small and large intestines are on the left palm. The foot is similarly divided, as is shown in the right photo of a teacher instructing a class on foot acupressure. Unfortunately, the labels are invisible, but the existence of symbolic organs around the plantar surface of the foot are easily appreciated.
There is an extremely useful site on the web, which not only explains acupressure in non-scientific terms, but even has a clever applet where you identify the part of your body where there's trouble, and what the nature of the trouble is. It's worth a look!
In acupressure, as in many of the therapies discussed herein, the emphasis lies in allowing the body's own self-healing abilities to manifest themselves, rather than introducing foreign substances which affect different people differently and which often exert toxic side-effects (the principle behind allopathic medicine). This is why the descriptions of some techniques sound similar - most emphasize re-establishing the body's homeostasis, especially involving chi (Chinese - qi). In contrast to the beliefs of some, chi energy has been accurately measured, using a variety of techniques and under many conditions. The existence of chi is not arguable, only the techniques for restoring its balance.