Internal force refers to sensitivity and endurance, and can also refer to qigong.

Qigong is divided into two categories, one is hard qigong and the other is soft qigong.

Hard qigong is more common, that is, the foreign kungfu you mentioned in China, such as Shaolin Boxing and Cai Lifo (Nanquan), all focus on practicing hard qigong. Hard qigong, whether offensive or defensive, will be full of luck to play hardball.

Contrary to hard qigong, soft qigong advocates that "people should follow others instead of themselves". When attacked, they will absorb and unload each other's strength. Practitioners are extremely soft, and hitting them is like hitting a hanging cloth, so it is difficult to hurt them. Soft qigong is like a whip when attacking. It does not advocate hard attack, but it must be fast. Tai Ji Chuan, Taixu Boxing and Wing Chun Boxing all practice soft qigong. Soft Qigong also has a good health preserving function, and Tai Ji Chuan and Taixu Boxing are the best examples.

Generally speaking, hard qigong is easier to practice than soft qigong, but it is certainly not as effective as soft qigong, and improper practice is easy to cause internal injuries. People who practice qigong breathe differently from ordinary people. Most people breathe with intercostal muscles, that is, with lungs. People who practice qigong breathe by the abdomen, that is, they take the abdominal muscles as the initiative and drive the intercostal muscles and diaphragm to breathe through the expansion and contraction of the abdomen.