Posted by: Jack Mankin (MrBatspeed@aol.com) on Fri Mar 4 12:33:02 2005

>>> If the swing is purely rotational, then why do most hitters back foot jump off the ground or get drug forward at or just before the point of contact! There is no such thing as a purely rotational force. Rotation is created by a linear movement that has an axis. For example, a tetherball doesn't rotate around it's pole until it is hit forward by someone and then it only rotates because it is connected to it's axis (the pole) by a string. There must be linear weight shift to maximize the torque that occurs when the front heel sets down.<<<

Hi Matt

First of all, when discussing what generates rotation of the body around an axis, we must keep in mind that there are a number of different concepts and forces to consider. For example, torque is applied as the back-leg drives the back-hip forward around a posted front hip. Or the extension of the led-leg driving the front hip rearward, which produces rotation around a stationary axis (the spine). In either case, this rotation comes from torque and has nothing to do with forward momentum being converted into rotational momentum.

Second, hip rotation can be generated by the contraction of muscles in the pelvic and lower-back region without any linear movement of body mass. In addition, many believe that linear momentum attained during the stride is also converted into rotation. However, this raises many questions.

(1) Why do we assume that the linear momentum transfer will rotate the hips counter-clockwise (right-handed batter)? If the hips remain fairly closed during the stride (parallel), there would be as much tendency for the momentum to cause the hip to rotate clockwise as counter-clockwise.
(2) When the linear momentum vector is directed “in-line” (“n” factor = 0) the momentum vector of the hips is directed into (and absorbed by) the lead leg. --- Shift your hips into a wall and see if there is any tendency for them to rotate.
(3) If the batter should stride with the hips (say) 20% open (“n” factor = 20 degrees), then only about 18 % of the hip’s linear momentum could be converted into hip rotation. Since the amount of momentum from a soft stride is small to begin with, more stands to be lost striding with the hips open than gained.
(4) If linear momentum is necessary for rotation, what about hitters (like Bagwell) who stride rearward? Would the negative momentum subtract from rotation? Would Bonds’ axis fading rearward during the swing (negative momentum) be subtracting from his power?

Matt, below is another post I recently wrote on this topic.

Jack Mankin
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Hi Mike

I do not recall Bagwell's 1994 stance. I would assume your point is that he had his best year while taking a forward stride instead of his present backward stride. I have no problem with your conclusion. Some hitters may very well perform better with a forward stride.

I do have a disagreement with thinking hitters like Bonds use the stride to obtain momentum for the swing. Linear momentum is the product of mass and velocity. Mass with little or no forward movement has little or no momentum to transfer. Hitters like Bonds may pick up the foot and place it five or six inches forward, however, there may be little or no forward movement of the axis (body mass). Therefore, there is little or no linear momentum to be converted into rotational momentum – if that were even possible.

Even with hitters like Brett who take long strides with a lot of forward movement, I do not believe the transfer of momentum plays the major role in their hip rotation. The major part of their hip rotation comes from the pelvis being thrusted around by the muscles in the thighs, hips and back – not the transfer of momentum at toe plant.

Try it for yourself. Stand up and take a long stride with your hips closed and see how much the hips tend to rotate without using the muscles to thrust the pelvis around.

Jack Mankin