Posted by: ray porco (rporco@verizon.net) on Sun Jul 3 19:28:51 2005

> How exactly do the legs function in the swing? Does the hitter consciously straighten the front leg and consciously push with the back leg, or are these natural occurences due to sound early mechanics? <

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Hitter,

I posted the following at another site, quite a while back. If it’s too scientific for you/anyone, skip the next paragraph, but please read the rest.

*****Studies of multijoint arm movements have demonstrated that the nervous system anticipates and plans for the mechanical effects that arise from motion of the linked limb segments. The general rules by which the nervous system selects appropriate muscle activities and torques to best deal with these intersegmental effects are largely unknown.
During multijoint limb movements, rotational forces arise at one joint due to the motions of limb segments about other joints. Central control signals to muscles are adjusted, in a predictive manner, to compensate for interaction torques-loads arising at one joint that depend on motion about other joints.
There is a dual role of proprioception in controlling multijoint movements; that is, to provide important cues both for the predictive control of interaction torques and for the synchronization of adjacent joints even when interactive torques are very small. These findings support the idea that proprioceptive input is used by the CNS to update an internal model of limb dynamics that adapts the motor plan according to biomechanical contexts.*****

A simple experiment:

Take an athletic stance (much like a middle linebacker – not a baseball stance). Make sure your feet are under your shoulders or slightly wider, and that your knees are slightly bent.

Now, think ONLY and move ONLY the body part that I say.
“Straighten your left knee”

What happened? Did your left hip rotate rearward?

Now get back in the original stance.

Again, think and move ONLY what I say.
“Turn your right knee down and in”

Did your right hip move forward, but not as much as the left did rearward?

And finally, now back to the athletic stance and again think only and do only what I say now.
“Rotate your hips to the left”

What happened to your left knee? What happened to your right knee?

What caused what?