From what I am observing through study of various high school/travel pitchers this year and looking at them in high speed slow motion perhaps the greatest potential for increased speed lies in slight alterations in mechanics relating to the position of and release sequence of the the upper body (shoulder, upper arm, elbow, forearm, wrist and fingers). Notably pitchers whose throwing shoulder did not continue to lead the way after heel plant but quieted to allow the rest of the arm to whip through seemed to throw hardest. I am going to work mechanics with my DD (who is only league 9) before I consider strength training or weighted balls. I think more speed potential is found in trying to uncover the mechanics of those who seem to easily throw hard.
lhowser, I agree. Pitchers that throw hard with little effort are the result of high efficiency in their motion. They use every point of resistance in the chain to whip the ball through at release for maximum velocity. On the hitting side, a five frame swing is used as the standard of getting the bat to the ball. On the pitching side, I believe the three consecutive frames starting where the arm is at the 7 o'clock position, then 6 o'clock and lastly at 5 o'clock indicate the whip necessary to throw the ball at or over 60 mph with spin to make it move, IMO. Toggle through with Quicktime or RVP of the high level pitchers and all of them can get this three frame motion of IR. The pitchers I work with that are throwing 47 - 52 use four frames to get through this area of the motion. lhowser, keep us updated with your progress in finding the "greatest potential for increased speed lies in slight alterations in mechanics relating to the position of and release sequence of the the upper body (shoulder, upper arm, elbow, forearm, wrist and fingers)." I believe you are looking in the right direction.