I was just thinking how much emphasis is put on to turning the leg, but in the same time no one speaks about the back. I mean if the lower back is not locked whats the point on turning the leg? What i mean is if the lower back is loose we will turn the hips, but this wont translate into turning the torso and at the end we will punch only by pulling with the back muscles or even worse only pushing. See for example how Joe Louis has always perfect position of his back and how fast and easy he moves. Than it comes the question of being loose in order to spare energy. There are different types of muscles and they love it different The erectors in the back don't love to move, they love to be under isometrical load. Here i have an other question. If we stay erect we can be loose in the lower back and still be in balance, but what about the slips or when we are in small crouch or the legs are not direct under us? For me if the back is loose we will never engage the hips and the hams so it will once again result in slow movement coming only from the back. There will be leaning and no balance.