Drilling jing is an offensive jing that twists as it penetrates. When your hand touches the opponent's body, your arm and hand rotate clockwise or counterclockwise in a screwing motion, which makes the power penetrate more deeply than with a regular attack.
The power, which is generated by turning the waist and shoulder, is usually directed forward, although it can also be used sideward. The fist, finger, or knuckle is usually used for attack, frequently against vital cavities. The muscles must be tensed somewhat to direct the jing and to ensure that it penetrates, and also to protect the hand against injury. Also, your yi must be concentrated inside his body in the organ or cavity being attacked. Drilling jing is also occasionally used to pull your arm out of the opponent's grasp. Here too the shoulder and waist are the sources of the jing.
Because drilling jing is used in both external and internal styles, many training methods have been developed. One of the common ways used in external styles is to drill your fist or knuckle into a bucket of mung beans. (Mung beans are used because of their medicinal properties.) With practice, you will be able to drill deeper and deeper. Later, sand can be used in place of beans. Punching bags are also popularly used for drilling training. Click to learn how Chinese medicine treats Chronic Bronchitis.
Taiji uses less muscle than external styles, so the training approach is different. One method uses a thick layer of soft material, for example, tissue paper on a table. The fist is pushed down with a screwing motion. The muscles should be relaxed as the yi strives to extend the jing to the surface of the table. When you can bounce the jing off the table, increase the thickness of the material. The thicker the material is, the greater the drilling power required. It is important to also do this exercise horizontally.