the MLB/high level pattern BB swing does have a back foot push as demonstrated by among otherd Yeager ground force/force plate measurements. Yeager has a website and DVD;s and has also described things in several posts at SHAWN's old site, Shawn may be able to provide a link.
and as Yeager points out the early phases of the MLB swing include back leg load and back leg push and are very similar to overhand throw.
The same thing is seen in motionanalysis as with:
Bat Speed -- Baseball Hitting Forum
"The forward swing is then initiated at the ground with the application of force to the back foot. As force is applied to the back foot, it creates a linear shift of weight, at the same time, their is a release of rotational energy around (rotating) from the front foot up to the hip of the front leg (the heal of which has dropped during the linear/rotational shift, to provide a solid front side to hit against)."
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An important thing to understand is that what is meant by PUSH is a force that uses the back foot as a base to accelerate the center of gravity of the body forward on line.
This does not say HOW/WHAT muscles produce the force.
In the MLB pattern, the early part of the "positive move" is by a push mainly from spreading the legs (leg ABduction).
later there is eversion and extension of the back foot.
The "PUSH" is not actively/primarily by back leg extension at the knee.
There may be other "rotational" patterns besides the MLB pattern which do not have this sort of sequence/push
and as Yeager points out the early phases of the MLB swing include back leg load and back leg push and are very similar to overhand throw.
The same thing is seen in motionanalysis as with:
Bat Speed -- Baseball Hitting Forum
"The forward swing is then initiated at the ground with the application of force to the back foot. As force is applied to the back foot, it creates a linear shift of weight, at the same time, their is a release of rotational energy around (rotating) from the front foot up to the hip of the front leg (the heal of which has dropped during the linear/rotational shift, to provide a solid front side to hit against)."
==========
An important thing to understand is that what is meant by PUSH is a force that uses the back foot as a base to accelerate the center of gravity of the body forward on line.
This does not say HOW/WHAT muscles produce the force.
In the MLB pattern, the early part of the "positive move" is by a push mainly from spreading the legs (leg ABduction).
later there is eversion and extension of the back foot.
The "PUSH" is not actively/primarily by back leg extension at the knee.
There may be other "rotational" patterns besides the MLB pattern which do not have this sort of sequence/push