Dear Steve,

I do not have the same clip of Rivera. The one I have is from earlier in the season. As I explained before I put the clips on the computer and use a program that allows us to measure displacements. My clip shows Rivera hips rotated 50% of his total hip rotation at foot plant. I think what you may be having difficulties with is determining/definition of foot plant. My definition is when the plant foot has made firm contact as evidenced by the loading of the foot/knee.

The point that Barry Zito seemed to be making (and I agree) is that it appears pitchers should strive to develop as much difference in displacement between the hips and shoulders as possible PRIOR to the shoulders rotating (linking up with hips). There are several very sound bio-mechanical and physiological reasons for striving to achieve this. Bio-mechanically, once the shoulders start to rotate, you ideally have connected to the hips at their (hips) point of fastest rotation. This is the essence of the kinetic chain principle. This principle (as applied to pitchers) has been described in several publications. Physiologically there is the stretch reflex, length of muscles for maximum contractile force and stored elastic energy (rubber bands). You said in your clip, the hips and shoulders start at the same time. This is in direct contradiction to these principles. One of the difficulties that most people have in communicating what they see to someone else each persons definition of hip rotation, when it starts, when it ends, etc.

Rivera has a significantly different delivery than Nolan Ryan. He is much more over the top which accounts for his lifting the back foot up and off the rubber so soon in his delivery. Ryan was longer horizontally (lower release point). If you look closely, you see that as the knee drops from its highest point, Rivera leads more with the heel (preparing to get over the top more). Nolan lead more with the side of his foot (flatter delivery).

Rivera also does not develop a great deal of differential between his hips and shoulders. He relies more on staying erect and using more of a rocking motion (hips lead the upper body more than Ryan).

One of the greatest pitfalls in these types of discussions is trying to prove a point based on personal interpretations and data samples that are small (in this case 1). How do we not know that Rivera has 90% fast fibers and throws 95 (although I thought this season his MPH was lower than past seasons) vs say Bartolo Colon who might have 50% fast fibers and throws 98 MPH or someone else who……etc.

My point is that basic principles of bio-mechanics and physiology support the concept of hips reaching maximum velocity and displacement before the shoulders turn. I have yet to see any studies or sound principles that contradicts this.

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