Posted by: Jack Mankin (MrBatspeed@aol.com) on Sun Jan 27 13:08:07 2008

Hi All

How that we have discussed the Weight Shift - Truism or Fallacy
question, how let us turn our attention to discussing the principles that induce hip rotation. I will open the discussion by asking the following question.

Truism or Fallacy - When the forward movement of the body gained during the stride is blocked by the lead-leg, the linear momentum attained causes the back-hip to rotate around the blocked front-hip -- like a gate swinging on hinges?

I addressed the above issue in an earlier post. I am placing an excerpt from that post below along with a supporting video clip. You may disagree with my conclusion. I only ask that you provide supporting evidence for your disagreement.

(Excerpt from earlier post)

Your post raises a question that has been debated for decades - What forces are at work that induces hip rotation? - on this question, the gurus are divided into 3 main camps.

Camp (1) - As the batter strides, he transferees his weight forward to a firm (posted) front side. As the linear progression of the hips is blocked, its linear momentum is transferred into rotational momentum that causes the back-hip to rotate around the blocked front-hip. - (Axis of hip rotation is around the front-hip.)

Guru, the theory of your post would fit into this camp. A longer stride generates greater linear momentum that produces a more powerful rotation of the hips.

Camp (2) - The Middle-Out Theory. -- As I understand it, this theory contends that hip rotation is induced solely from the contraction of the muscles in the pelvic region. The legs contribute little or nothing. It is hip rotation that straightens the lead-leg and forces the "L" in the back-leg. -- This would seem to downplay the importance of weight-shift. - (Axis of hip rotation would be around the center of the hips - the base of the spine)

Camp (3) - This theory contends that hip rotation is induced from a combination of muscle contractions in the pelvic region and torque supplied from the legs applying force from opposing directions (back-leg driving forward & front-leg pushing rearward). This theory also downplays the need for linear weight shift to induce hip rotation. (Axis of rotation - the base of the spine)

I am in Camp (3). I do not think the blocking of linear momentum is transferred into rotational momentum. Therefore, I do not think the length of a batter's stride or the amount of momentum derived is a major factor in generating hip rotation. - I will explain why below.

The same physics principle that governs the rotation of a bat about a point also governs the rotation of the hips about a point. - For decades, we were told that the batter should drive his hands and knob at the ball. We were told that once the linear progression of the hands slowed to a stop, the bat's linear momentum would be transferred in rotational momentum, which would accelerate the bat-head around to contact (Like the crack of a whip).

As this clip - No Whip Effect -- demonstrates, there is little to no transfer of linear momentum into rotational momentum to accelerate the bat-head as the hand's linear progression is blocked. The same principle holds true with hip rotation. -- There is little to no transfer of linear momentum into rotational momentum to induce hip rotation as the hip's linear progression is blocked.

Supporting video clip -
What induces hip rotation?

Jack Mankin