One should be able to use Tai Chi in self defense at this point in time. As the chi sinks, the upper and lower body become more of a unit. When this occurs, one can begin to develop what is called internal power. Silk reeling involves three aspects. They are stretching, twisting and relaxing, all simultaneously during each movement.
People tend to cut their body into two parts which prevents any chance of silk reeling.
Therefore, if one sinks the chi making the upper body empty and the lower body full, one will link the body into a connected piece which when taught to silk reel, will produce internal power. This is what the Chen style considers to be true power. This level is a good Tai Chi player. Most masters are at this level. The player can sink the chi down always at any time and therefore experience true relaxing.