Although the term 双重 Shuang Zhong can be literally translated as "Double Weight", actually its meaning is much more articulated and not necessarily related to the distribution of the body weight in both legs.
Wang Zong Yue writes: "双重则滞" Shuang Zhong Ze Zhi, "Double weight leads to stagnation".
To understand the concept of 双重 we must inevitably consider the theory of Yin and Yang. Chinese internal system bases its alchemy on the harmonization of these two elements. We must learn to clearly distinguish the energetic and physical quality of our actions.
In the Yi Jing the concept of Yang is generally represented by a solid line “—" while the concept of Yin by a broken line "- -". A possible representation of Yin Yang is "- -" “—" combined, that is the co-presence of full and empty.
In the context of the "double weight" we will have two equivalent manifestations “—" “—" or "- -" "- -". From the point of view of Chinese internal system, this condition will lead to a weakening and stagnation of energy.
In the continuous transformation of posture during a movement, full and empty have to balance in accordance with top, bottom, right, left, forward and backward. To better understand this example, let's consider the classic position of Tai Ji Quan "Brushing the left knee".
In this case, the left leg will be mainly Yang while the right leg will be Yin. The left arm will be predominantly Yin while the right arm will be Yang. The upper part of the body will be mainly Yin while the lower part will be Yang. The back will be predominantly Yang while the front will be Yin.
The analysis of Yin and Yang of the postures must be carried out in accordance with the function of the gesture and can only be implemented considering a specific frame of a movement. Because the energies are in continuous transformation and harmonization.
Generally speaking, the physical sensation of 双重 is that you can no longer move your body freely. It is often referred to as 刚 Gang (Stiff), 没有 根 Mei You Gen (Without roots) or 散 力 San Li (In a state of dissipated force, without coordinated energy).
To avoid this situation, the classics suggest to reflect on the rule 不丢不顶 Bu Diu Bu Ding (Do not disconnect - Do not go against). Educating the body to move maintaining an organized structure through the six harmonies and learning how to absorb the energy of the opponent are the two fundamental aspects to avoid falling into this mistake.