Re: kinetic chain
>>> Hi all. I would like to learn about what is known as the kinetic chain. I heard this was the place to go to ask. I realize the subject may be a far-reaching one, but I'd just like to know the basics. Your help is greatly appreciated. Chris <<<
Welcome to the site. I wrote a post below that pertains to the subject of your post. I am re-posting it so that you and others may respond to it. --- I refer to the kinetic chain as the mechanics of developing rotation around a stationary axis. Body rotation provides energy for the swing, but how much of that energy is converted into bat speed depends on the efficiency of the batter's transfer mechanics. - Below is the post.
It is quite obvious to anyone who has studied the baseball/softball swing that the hips are ahead of the shoulders or hands at the start of the swing. The hips start to lead the shoulders well before the swing is initiated. In the Frame-by-Frame section of the site (Swing Mechanics) I wrote, "The batter has rotated (inward turn) his lead shoulders away from the pitcher." So the hips already lead the shoulders by 20 to 30 degrees as the batter prepares his launch position (look at Frame #B).
Frame #C shows that some (not all) batters develop even more separation during their stride. I stated, "The lead knee has started rotating around toward the pitcher;" (not all - after Barry Bonds' stride his lead knee still points more toward the plate than the pitcher). This means the hips now lead the shoulders by approximately 30 degrees. All of this occurred before the swing was fully initiated. From viewing the 'Frame-by-Frame' section, everyone should see and understand that the hips lead the shoulders at the 'start' of the swing. ---But we must also remember that at the 'finish' of the swing, the shoulders will have rotated past (and now lead) the hips. And after full initiation, the hips and shoulders do rotate at the same time. When studying the swing in frame-by-frame motion, you can really see this happening.
I used the term "unison" to denote mechanics that during initiation have all the muscles in the legs and torso are contracting in unison to drive shoulder rotation. This is to distinguish it from "sequential" mechanics where the batter first contracts the leg muscles to rotate the hip (while holding the shoulders back) and then later fire the torso muscles.
Note: There is a 3-stage type of mechanics being taught where the batter is taught to (1) stride, (2) use the leg muscles to fully rotate the hips while keeping the shoulders closed (3) fire the arm and torso muscles to bring the hands and rotate the shoulders. --- I refer to the hips rotating while keeping the shoulders closed (no load rotation) as "freewheeling." For there to be a kinetic chain (or rubber-band effect), continuously energy must be supplied from the ground upward to rotate the shoulders. This means, all muscles in the legs and torso must be contracting in "unison, not "sequentially."
Although all the muscles are contracting in unison at initiation, the hips will still rotate a few more degrees ahead of the shoulders due to the increased load of accelerating the upper-body mass and overcoming the inertia offered by the bat to acceleration - not from sequential timing.
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