Line up the forearm and rear calf

What does it mean by lining up the forearm and rear calf? There are 2 ways:

1. The forearm and rear calf can on the same line, but separate into two sections.
2. The forearm and rear calf can also be on two parallel tracks.

Refining Flash the Back

Overall, flash the back is used to throw someone over the top. We started training with a stick to understand the idea of a lever.  The left hand is a pivot and does not move at all. The right hand holds one end of a stick, it starts at a location front of my body. It stretches against the non-moving left hand, and goes downwards towards the floor, and then goes up on the other side, all the while stretching more. At the same time, the right move from the front to the back, it is used to pull the stick. We have to imagine that the other end of the stick has a heavy load. We catapult the heavy load over our head and throw it. As my right hand stretches down and back, there is a point where the opponent's power disappear, and we need to quick switch to the other side with the left hand continuing the overall vertial rotating motion. The use of the stick makes it very clear how the lever works here.

Now without the stick, we need to rotate the dantian area. We need to thrust the dantian to the left and up to go around the top. The stick is like between the left hand and the right foot. The movement of the right foot allows the left hand to turn over at the dantian.