Regarding roundhouse kick middle section breaking. I have heard of two methods to perform this task. 1) Break with the ball of your foot assuring that the board grain is vertical and facing at a downward angle; the other 2) the top of your foot with your foot held straight for the impact. Which is the preferred or prescribed method? What are the advantages and disadvantages? Where does the techniques derive respectively?
Round kicks may be performed two ways; striking the ball of the foot or striking with the instep (top) of the foot. The ball strike is more powerful and may impact with tremendous force with little chance of damage to the foot, and it gives more penetration. For example, the foot may extend behind a blocking arm and still hit its target. The instep strike has move range, is easier to use, and is a little faster, but it is easier to block and the instep has many fragile bones and is easily injured.
For breaking, the ball strike is best.
For sparring, the instep strike is usually preferred.