Energy
Yesterday AM was a good class, for me anyway. The morning classes tend to be a little less intense, though not necessarily. (It's less intense unless Sensei decides to throw you, er.. wake you up.) For at least the first year at the dojo, I would sometimes literally run out of energy, not only being winded, but not being able to move enough for the technique to be effective. Of course, I was "doing it wrong" and I was out of shape. I'm still not in the best of shape aerobically, and oh yeah, my back hurts--not good! But now I have an idea of what it feels like to use ki and not muscle. All the motion originates with your center, and in the hips. The energy ideally just radiates through the rest of your body like electricity. To do this you need to have the arms relaxed and the spine flexible. Your body moves more like a single unit and your arms and hands should (almost) never be moving without your center being in motion, because the center is driving the technique.
So a primary exercise is being able to maintain relaxation. This lessens the amount of energy required, and by the end of class you may be hardly winded.
So a primary exercise is being able to maintain relaxation. This lessens the amount of energy required, and by the end of class you may be hardly winded.