It is very common for students of Taijiquan to lose their root when they begin training Fa Jin or power manifestation. When I watch my students first try punching the BOB (Body Opponent Bag) with power or striking with Taiji Cane, I often see their heels come up and sometimes even leaning that compromises their center. Pay attention when learning Fa Jin. Sink. Feel like your legs are sinking or being screwed into the ground with a spiraling energy. Note that when you sink not only will your root be stronger, the power of your punch or strike will be greater.