Pain is also relatively easy to quantify, and progress can be measured fairly simply. For these reasons, physicians trained in Medical Acupuncture treat musculo-skeletal pain conditions as one of their early applications of their newly developed skills.
, also commonly spelled ch'i, chi or ki, is a fundamental concept of everyday Chinese culture, most often defined as "air" or "breath" (for example, the colloquial Mandarin Chinese term for "weather" is tian qi, or the "breath of heaven") and, by extension, "life force" or "spiritual energy" that is part of everything that exists. References to qi or similar philosophical concepts as a type of metaphysical energy that sustains living beings are used in many belief systems.