The Classics describe transferring energy through the legs as though they were springs. When avoiding, the front leg moves the one’s center back; when applying, the weight launches it forward. The center should never move so far as to uproot either foot.
During Tai Chi Chuan, the practitioner shifts his weight from one leg to the other dozens and dozens of times. Some of these transitions between yin and yang are fairly straightforward, others are slightly modified or unique, but all hold a common theme: the yin leg must be structurally stable enough (yang) to accept the energy from the yang leg, and the yang leg has to be relaxed enough (yin) to listen to the needs of the transition.
This is evident when preparing to push from a Bow & Arrow Stance. While coiling on the back leg, it should feel as though you are sitting back onto a stool, but there should still be some mobility in the hip and knee joints. The front leg should be fairly empty; however, some structure is required (bent knee aligned with the foot) for balance and also so that it can receive the weight transfer properly.
Remember also that a good set of springs is only as good as the placement of the anchors. The integrity of each foot’s connection with the earth will affect the strength and direction of your energy. If your Bow & Arrow Stance is too long, your push will not go in the intended direction. If too short, you will not be grounded enough to make an effective push.
Take a few minutes before class to practice shifting your weight from leg to leg very, very slowly. Listen as one leg fills up and the other empties. Do both feet remain completely grounded? Are you moving in the direction of intent? When sitting back, does it feel as though your legs will push in the direction you want to go?
Find your springs.