The Changing Tendons Exercise (Yi Jin Jing) is another form of exercise handed down from ancient times. In Chinese yi means change, jin means "tendons and sinews", while jing means "methods". This is a relatively intense form of exercise that aims at strengthening the muscles and tendons , so promoting strength and flexibility, speed and stamina, balance and coordination of the body. This exercise pays great attention to the coordination of movements, respiration and mind so as to guarantee that qi circulates freely and smoothly. As with most exercises, there is an enormous variety in form, the most popular being the "12-postures of Changing Tendons" devised by Pan Wei in the Qing dynasty (AD 1644-1911). See the picture below for reference.