“Flesh gives birth to flesh, but the Spirit gives birth to spirit.”
The verse shows two kinds of life—life of flesh and life of spirit. They are totally different in nature. Life of flesh never becomes life of spirit by means of improvement or modifications.
In traditional Chinese Kung Fu, there are two fundamentally different kinds of forces. The mechanical force is called Li (力) which derives from joined efforts of muscles, bones and tendons. Li is commonly observed at elementary level of Kung Fu. This is what we are familiar with and called ‘strength’.
In contrast, non-mechanical force is ‘energy of Qi’ or called ‘Neijing (內勁)’ which derives from joined efforts of spirit and Qi. It is the source of power employed in advanced Kung Fu.
Just like life of flesh and life of spirit, these two forces are completely different in nature. Li can never become Neijing by increasing its amount or by enhancing its skill level.
Proficiency in martial arts is not determined by the level of difficulty or complexity of forms per se, but by the nature of the force employed.
Although both Li and Neijing co-exist in our body, they are mutual exclusive in use. They cannot be applied at the same time. The more Li energy is being used, the less Neijing can be being released, and vice versa.
This is because the ways they generate and use follow different, or even contradict laws, just like life of flesh and life of spirit.
The amount of Li force you can be employed in Kung Fu depends on several variables such as resilience of muscles, strength of bones, speed and timing of attack and so on. An effective way to enhance the Li force is to exercise your muscles and bones by applying increasing pressure on them (weight training, gym exercises, etc.).
On the other hand, the amount of the Neijing force depends on the degree you can ‘Song’ （relax in positive, active sense）.
The Li force is observable when it is employed. At the point of attack, you must tighten up your muscles to unite your strength and create an explosive power. In this process, the state of your muscles changes from soft and loose to tight and tense. The effectiveness of Li follows the principle of leverage. In combat, the point of contact is the point of attack. The combatant who can make better use of this pivot point has a greater chance to defeat his or her opponent. The muscles, your fists and legs, are weapons themselves.
Unlike the Li force, Neijing is invisible and hence unobservable when employed. The pivot point is not necessary. At the point of attack, you must ‘Song’ yourself to release all Qi energy and direct it towards the target. The contact point only represents the gateway to conduct Neijing to the target. Your muscles are channels of Qi only.
The Kung Fu component of Li force is limited by your physical condition. When you pass your prime age, your Kung Fu ability will pass the optimum level, too. The degree of Kung Fu will decline when muscles and bones are not as strong as they used to be. On the other hand, the Kung Fu of Qi continues to grow as long as one lives. Qi energy becomes stronger despite the aging process.
Tai Chi Chun is the kind of Kung Fu with energy of Qi.
Tai Chi Chun was first made known not due to its values and functions to keep fit or stay healthy, but its powerful effect as Kung Fu. With Tai Chi Chuan, Yang Lu Chan defeated all competitors and became the Chief Kung Fu Coach of royal guides and personal coach of the royal family of the Ching Dynasty hundreds years ago. He got a name of ‘Invincible Yang’.
Nowadays, millions of people in the world practice Tai Chi. But persons who know its Kung Fu function are rarer than pandas.