Doing yoga or tai ji or any other activity where we are standing or moving from foot to foot, one basic set of actions that we can learn is how to activate the feet. The purpose in doing so is to create a stable foundation so that we can do what we are trying to do whether it is holding a pose or doing something with our arms or simply balancing on one foot.
At a muscular-skeletal level, any one muscle generally attaches one bone to another, in the process crossing one joint, two joints or many joints. A muscle can be used to change or maintain the relationship between the bones that it connects. So that we can control our muscles and via them the bones that they relate, we may find it helpful to give the muscle that we are trying to activate or relax a stable foundation. If we make one of the bones to which it attaches stable, then we can use said muscle to change or maintain the relationship we desire.
Working from the ground up while standing, if we learn to stabilize our feet, ankles and lower legs, then the muscles that cross the knee joints have a stable foundation from which to act on the thigh and pelvis. We can use these muscles then to position our thighs and pelvis. Our thighs and pelvis then provide a foundation for muscles that cross the hips and span the lower back and spine. Those then in turn act as foundations for the ribs, shoulder blades and arms.
For myself, I have found that making the feet, ankles and lower leg strong and stable makes it easier to release the back of my thighs while doing a forward bend or make it easier to relax my hips or create space in them depending on what I am trying to do. In general, making my feet strong while standing makes it easier for the rest of my body to do what I want it to do with a minimum of effort. I find that just activating my feet doesn’t help. However, activating feet, ankles and lower legs does make it easier to do what I am trying to do.
Generally the first step I teach in activating the feet is rolling the shins outwards. While initially I thought this happens mainly in the ankle, I recently realized that what I am actually teaching people to do is rotate the shin at the knee joint. In so doing the two lower leg bones act like a wrench on the ankle bone (talus.) The back part of the foot including the instep are then forced into a shape where the inner arch is naturally lifted. I think I came about this action as a way of dealing with my partially flat feet.
To practice this action I normally have people slowly and smoothly rotate their shin outwards and inwards with their feet about hip width, parallall with knees slightly bent. The slower and smoother the action the more you improve control and the ability to feel your feet.
The next action I add on to this (and it can be done in time with the breath-rolling outwards on the inhales, release smoothly on the exhales) is to press down through the outer edge of the foot. Do this without lifting the inner edge. The next step is to then add on the inner arch. This means pressing down through the base of the big toe. You can focus on pulling back and down on the base of the big toe while rolling the shin outwards and pressing down through the inner arch. Practice by moving with the breath.
As you do this action notice how your shin and knee move together. At the end of the action you may find that your knee points in roughly the same direction as the toes. As a game you might try aligning your knee with your big toe, second toe and then third toe all by feel. Do first and then check afterwards to calibrate your senses.
Once you have the hang of these actions, practice holding the foot active. Now do it with the minimum effort necessary. See how much you can relax the feet while still engaging the arches.
One final action for the feet is to lift the center of the outer arches. You’ll feel this along the side of the lower leg.
These actions all together involve muscles within the foot as well as muscles that cross the ankle. To make the foot and lower leg solid, stable, practice then squeezing the bones of the lower leg from all four sides using the muscles of the lower leg.
Practice activating and releasing in time with the breath (inhales activate, exhales release) and then practice holding for about five breaths.
the goal is to be able to do this at will without having to think about it or try too hard.
Then you can use this action as part of any standing pose or standing movement.
In warrior 1 (virabhadrasana), parsvotanasana, revolving triangle (pravrtta trikonasana), you can activate your feet and try relaxing your hips to allow your pelvis to naturally face the front.
In warrior 2, side angle (parsvokonasana), triangle (trikonasana) you can try using your front foot as a foundation for rolling the pelvis open.
In any pose where you are grabbing a foot it may be helpful to make that foot active, particularly if it is not on the floor.