Keep the energy moving

Sifu continually tells us that the energy must move. The cycle has to be continuous. I have listened to this and thought, "Ok, the energy must keep moving." But, I have realized that I don't comprehend this yet. When someone applies force to my arms, I meet the force and my abdomen becomes very full and hard. Sifu said that the fullness needs to be there but it needs to move to the mingmen. I need help understanding this. The abdominal fullness remains; even though I move to open the mingmen. Any body, every body, HELP! ;)