THE BASE of the PULL and the importance of DOUBLE SUPPORT
This graphic ilustrate how important is to be as far posible from the Base in order to achieve the long pull.
It is important to understand that the base will change depending  on the position achieved by thrower before and durring the release.
This graphic show 3 diferent locations for the  base of the throw.
Yellow = Arm Thrower - No that  much pull the Base is located at the level of the Hips.
Green = Arm Thrower + some Hip  - Feels the pull but can't  tranfer energy from the run up to the throw the Base is located at the  Knees.
Red = Arm Thrower+ Hip + Momentum  from the run up. -Feels the  pull, get the tranfer of energy from the run up to the throw the Base is located  at the Left "Plant" Leg. The right leg stay pasive and  create balance that allow the delay of the arm strike.
Take a look  at the positions of   ( Tom Petranoff, Jan Zelezny) in the following pictures but  keep in mind that this is a quick and fast action and that everything  happen in fractions of a second. 

I just want  to show here how  important is to be in the right position previous to take any action with the spear. This are the basis for the long pull (1) The thrower needs  to keep the arm still and as far back as posible, (2)  wait for the impact of the plant leg and (3) needs to achieve the double support durring the pulling action..
Look at the full body extension when the left leg  made contact with the ground..
This position is the same as the red line shows.
The C position.
The Solid  left leg, and the action of the right leg  that makes posible the  transfer of energy from the  impulse  creating  the elastic reflex.  The left arm to the rib cage blocking the left side.
Take a closed look  the right leg still in contact with the ground and the javelin is just released.
Look how Jan Zelezny get into the same position ->Red line of the Graphic Picture # 1. and how the right leg works to maintain the double support durring the release.
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