To fully understand why leech therapy works in such a wide range of applications, one must realize that the therapeutic activity of leech therapy (which is still not fully understood) is not based on a single mechanism of action, but on a combination of multiple effects. If conceived as a form of local drug therapy, a complex model would have to be used to explain the pharmacological action of leeching. The leech could then be compared to a drug that acts locally in a palm-sized region. It reduces the viscosity of the blood in that region while simultaneously dilating the blood vessels, accelerating the lymph flow, inhibiting platelet aggregation, blocking numerous mediators of tissue infection, and exerting local analgesic and anesthetic effects, thus minimizing the pain of treatment. The active role and sensitivity of the leech is a special feature of leech therapy. The leech is equipped with an extremely sensitive nervous system, which it uses to inspect the host and the host's blood. The dosage of secreted saliva is presumably adjusted in accordance with the leech's "preliminary examination findings."
Based on an understanding of its multifactorial mechanisms and aspects for its symptom-specif'ic application, leech therapy can also be recommended to treat rheumatic diseases and chronic pain syndromes of the musculoskeletal system.

Muscles make up over 42% of body mass. Assessment of muscle tension is a basic part of any medical assessment of diseases of the locomotor system. The 424 striated muscles constitute the largest parenchymatous organ of the human body. In musculoskeletal mechanics, the muscles form the link between static and motor activity, Nearly all diseases of the musculoskeletal system are characterized by impairment of muscle function. Muscle tension can be defined as abnormal variation between muscle tension and muscle tone. A quantitative classification of muscle tension can be useful when assessing the appropriateness of leech therapy for treatment of patients with painful chronic and vertebrogenic muscle tension.
Focal bands or zones of hardening within a muscle are classified according to the main muscles associated with them. In medical terminology, localized areas of hardening within a muscle are referred to as myogelosis. Myogelosis must be differentiated from actual muscle tension, in which a muscle group or cord exhibits a variable degree of muscle tension. Muscle tension is classified according to which the main muscle or muscle nearest the body surface is affected. The severity of muscle tension generally correlates with the response to local leech therapy.
Painful trigger points are important for treatment planning. Myofascial trigger points are important target sites for leech application. There are two types of trigger points: active and latent. Active trigger points exhibit pain spontaneously without application of external stimulus, whereas latent trigger points give rise to pain only on pressure. Moreover, trigger points must be differentiated from tender points. The 18 tender points used for diagnosis of fibromyalgia are not specific target sites for leech application.
Specific areas of myogelosis are useful for pain localization and should be evaluated carefully before leech therapy. Myogelosis is characterized by reversible colloidal changes within a muscle. If myogelosis persists for long periods of time, destruction of muscle fibers occurs in a process characterized by increased nuclei, loss of transverse striation, and degeneration of myofibrils.

When evaluating a patient, it is important to note that tonic and phasic muscles differ with respect to the types of contractility and metabolism associated with them. Pain, inactivity, overactivity, improper use, poor posture and trauma can lead to shortening of tonic muscles and to weakening of phasic muscles. The maximum isometric muscle tension in tonic muscle fiber groups is greater than that in phasic muscle fiber groups. However, tension build-up is much faster in phasic muscles. Loss of elasticity occurs in predominantly tonic muscle groups, and predominantly phasic muscles fatigue more rapidly.
Most skeletal muscles have approximately equal fractions of tonic and phasic muscles. The iliopsoas muscle is a good example of the shortening tendency of tonic muscles. Because of its proximity to various organs in the abdomen and pelvis, it very often shortens in response to functional isorders of these organs (e.g., diseases of the colon and urogenital tract). The iliopsoas muscle can easily be tested but is difficult to palpate, and physicians frequently forget to check for iliopsoas shortening. Shortening of the iliopsoas muscle plays a major role in many pain processes. In the lumbar spinal region, psoas shortening leads to chronic hyperlordosis, which is accompanied by the well-known symptoms of facet syndrome and Baastrup disease. Local pain in the hip region is not uncommon. On closer inspection, some of these cases turn out to be iliopectineal bursitis.
The muscles in the neck and lumbar region are most frequently utilized to maintain body posture. This constant use leads to typical pathological changes in the neck region, including palpable areas of hardening within the muscles and surrounding tissues, as well as reduced range of motion of neck and shoulder muscles. This frequently leads to the development of cervicobrachialgia.

The postural mechanisms for vertebral joints in the lumbar region have greater distances to overcome. A well-developed muscular apparatus is able to actively contract and support the body in order to counteract the normal lever effects on the lumbar spine that occur during daily activities.
If the musculature is impaired, passive postural and support mechanisms must bear the full brunt of' this lever action. In all pain syndromes characterized by the described signs and symptoms, the main goal of treatment is to break the vicious circle of symptom worsening
These reflex mechanisms often have such an enduring effect that limited range of motion and pain often persist long after the cause (e.g., disc herniation) has been eliminated. When included as part of a balanced physical therapy and therapeutic exercise program, local and symptom-specific leech therapy often achieves very long-lasting effects, which can be very useful in the initial stages of multidisciplinary therapy. Chronic vertebrogenic and joint pain syndromes due to degenerative rheumatic disorders and sports injuries are some of the many practical areas of application for leeches.