Hello,
My understanding is;
Do the exercise slowly and in a circle which in “toward harmony qi and Taiji” newsletter described as a means to relax. I think the slowing down is a process to allow us to compose the mind and to be mindful. Being mindful comes first, it is the mind that moves the qi and then the muscles. It is possible to most the hand and legs without being aware of qi or muscles, after many repetitions, it can become automatic without much need to feel your muscles. At present the idea is to do the exercise with minimum attention to the muscles because completely ignoring the muscles is not natural to you yet.
I have this idea that the mind moves the qi, which is the purpose of this set of exercise. In fact, it is the main feature and its best feature of this set to move and balance qi in the body. The hand and leg movements, and so is where the muscles come in, is to facilitates or induces the qi to flow. This is where the idea that we should not be lost by concentrating on muscles activities. In short, it is all mind and qi and forgets about the muscles. This is my way of looking at it.
The front ball of the feet should be sticking to the ground and a lot of energy is flowing there. What goes into the ground is replaced by fresh qi coming up at the front ball of the foot. Stay grounded there and be refreshed.
Brain advise in the video is relax and play around.