Wudang Tai Chi and Liang Yi concepts include the principle of “Qi” or energy-transformation. Qi is a power we can all use with our intentions. The mastery is about the efficiency of the Qi transmission.
I will try to explain it in the most practical way with ordinary bicycle gears:
From the inner movement
Like a bicycle we need a lower gear to get a feeling for faster movements or else it will over in an instant. This is the reason why Tai Chi is performed more slowly than Kung Fu. The correct speed comes from the control and mastery of each inner movement. However we do have few main principles about how slow and how fast we can be:
Breathing according to movements
Breathing generates power which we can use for our movements and basically we cannot move slower or faster than we generate power through our breathing technique. This is also why Qi Gong mastery is important for the understanding of advanced Qi transformation.
Relation of movements
We learn that all energy comes from the Dantian (energy center). Through our intention we can control Qi from the Dantian to our movements. Energy (Qi) is always divided in Yin and Yang. Therefore every movement has the according opposite Yin -> Yang, Yang -> Yin. To control Yin we also need to control Yang and to control Yang we also need to focus on Yin. This relation is the foundation of Qi transmission. However since Yin and Yang can never be the same value, it is the opposite. The inner movement can therefore never be in the same speed/power relation. Like the connecting chain in the bicycle gears. We generate more power over smaller gear wheels than with larger ones. Ignoring the relation of the gears and the connection of the chain can break the inner movement and make the energy transmission inefficient. The speed and execution of Tai Chi is therefore slow and interconnects with the relation of inner and outer movements.
The principle of energy transformation can be applied on everything. Tai Chi simply is one of the most common practice for further understanding. In Kung Fu for example we can use more power more quickly. Like the picture above shows us the use of the same power and the amount of achieved distance.
Now it should be more clear why “internal” masters practice Tai Chi very slow and execute Kung Fu explosively fast. These principles are essential for Wudang and any other internal martial arts. Often you see fancy Tai Chi and Kung Fu performances. While there is a lot of interpretation freedom, the principle of energy transformation cannot be skipped and it does show the mastery level of power and control.