Posted by: Jack Mankin (mrbatspeed@aol.com) on Mon May 17 18:33:09 2004

>>> Jack,

You have introduced the terms THT and BHT to describe "the most active hand at each point of the swing". You also note "in a good swing, pressure sensor pads on the bat handle indicate the hands are exerting a fairly even force".

I have studied these statements, and can reach only one conclusion: Your most active hand is merely that which APPEARS most active FROM AN OVERHEAD SHOT (italics intended).

Since the CHP is in a plane which is not perpendicular to the camera sight line, the hand which appears more active is always closer to the camera. Initially, top hand (higher) appears to circle around bottom hand. Finally, near contact, bottom hand (higher) appears to circle around top hand.

THT and BHT are visual cues to relate bodily action in an overhead shot perspective. They indicate nothing of hand force dominance - merely that hands are always in a push/pull relationship.

Is this observation correct?

Thanks,
Mike. <<<

Hi Mike

You stated, “I have studied these statements, and can reach only one conclusion: Your most active hand is merely that which APPEARS most active FROM AN OVERHEAD SHOT.” – First of all, we can safely say that the entire length of the bat (knob to the bat-head) is undergoing the same rate of angular displacement. Therefore, throughout the swing, each hand (on the bat) must also have the same rate of displacement as the bat.

However, even though the knob and bat-head have the same rate of displacement, the bat-head is obviously moving at a great angular velocity. This is because the bat-head is farther from the axis the bat is rotating about. Likewise, the angular velocity of each hand will depend of the point of rotation (axis) of the bat. When the axis of rotation is between the hands, the angular velocity of each hand would be the same. Therefore, your observation is true for most of the swing where the axis is more or less between the hands.

Note to all readers: There are four main axis of rotation in swing mechanics. The two we are concerned with in this discussion is the stationary axis the body rotates around and the axis at the hand-path where the bat rotates round. We are discussing the angular velocity of the hands around the hand-path axis.

As I stated earlier, the angular velocity of the top and bottom hand will be about equal when the axis is between the hands. However, there are two points in rotational transfer mechanics (at initiation and at the “hook” in the hand-path) where the axis is at (or closer to) the top or the bottom hand.

At initiation, the bottom-hand remains fairly stationary at the back-shoulder and serves mainly as a pivot point as the top-hand pulls the bat-head in an arc back toward the catcher. In this case, the axis of rotation is closer to the bottom-hand or knob. Therefore, the angular velocity of the top-hand is greater than the bottom-hand.

Just the opposite is true at the hook in the hand-hath. Although the hand-path is moving, the slower moving top-hand is now serving more as the pivot point for the lead-shoulder to pull the bottom-hand around (BHT). In this case, the axis of rotation is closer to the top-hand.

While doing swing research with a Motion Studies Computer System, we placed motion sensors on each joint of the body, on each hand and on the knob and bat-head. We got both angular displacement rates and angular velocities for each sensor anywhere in the swing. We could also study the trajectories (from one or more sensors) from any angle. – My understanding of swing mechanics was much enhanced from this study.

Jack Mankin