Huge bend = 100% straight bottom arm
No bend = 100% bent bottom arm
Every vaulter falls in between those two extremes. Because bottom arm straightens out doesn't mean they are applying force per say with bottom arm. The pole is just bending to max during the initiation of swing to flat back. On the other hand some are pushing very hard. Unless said vaulter and coach says what they are doing YOUR GUESSING!!!!!!!!! I'd be almost safe to guess if little bottom arm just after takeoff they can't push even if they say they are. If lots of bottom arm than yes they are pushing. To me most of the vaulters I see with little bottom arm off ground that try to push/extend just end up overly rowing hands and sitting in a chair to block out and check swing the jump.
Bubka was brought up. http://www.youtube.com/watch?v=L0P3H4iO1DU&sns=em
. First jump blasted no bottom arm off ground than it straightens out. One person can go he pushed it out another can go it straightened out as the pole bent.
As far as brad goes I don't think he is the same jumper technique wise today as in 2008. I was there when he broke the AR. This is the best video I could find on the fly traveling with bad Internet and time. http://www.youtube.com/watch?v=o_XIhp4RywA&sns=em
It seems his bottom arm goes straight near left leg cast to parallel to ground. Pole is almost near full bend as well. Was he trying or did his arm just straighten. Go do a 250 pound single arm bench press. Nice part is your friend is helping you lift the weight. (Pole bending). To logically think you are actually straightening the arm out on your own is the great mystery for me. Very few of us are that strong in a mechanical sense only in the elastic world can we produce high force outputs. Elastic movements win IMO. To me his 2008 AR jump is elastic. I can't say what he was trying to do but I would not call this him pushing out with the bottom arm.
I would also like to point out a tuck can occur on accident not by design or want. If the fire pattern of movements is off and an athlete is executing a movement either too long or even .02 seconds late to trigger the next movement a fold or break in the continuous movement can occur. I have seen Renaud takeoff and swing with no break in his hips over 5.70 from 6L. From full something is not lining up the same so he gets a pause. I'd be safe to guess its not on purpose. Id guess It's something his old and new coaches are trying to adjust. I'm not sure as are none of you who are not in their camp.
I would like to make the point in regards to switching to the bottom hand will increase pressing on top hand. I disagree. When you switch from one lever point to another the lever point further away from the pivot point is turned off or used lesser. Now I'm not saying this isn't or couldn't be used effectively in someone's model. I'm saying my interpretation of basic motion is only when pressure is constant can it be progressive. If you start with pressure on top arm than switch to bottom arm the pressure felt on top arm is greatly reduced. There was an interest article a few years back I read that talked about a similar concept. The Theory of when moving to inversion to do switch to bottom hand pressure to shorten the lever point thus increasing lift potential with the shorten bent lever. However most athletes I see who switch pressure to bottom arm just tend to flag away from the pole on the turn. Not effective!
Though the way I'm reading it may be wrong. My personal stance is any unwanted pressure with bottom arm will only cause inconsistencies in the rest of the system. Continuous movements can only occur with two fixed points (top arm and box) when you add a third or fourth chaos will occur and body parts will move in different directions to compensate. Constant pressure for me can only exist if the top arm shoulder stays closed (shoulders square) at impact and beyond. This is the basic fundamental movement i look for and coach.
If shoulders open so that top arm shoulder twists back than they must close to reconnect to pole. This action IMO is sometimes mistaken for bottom arm and top arm pressure (rowing). Then cue to hit the hands may be the cue to cause the shoulder to close but the shoulder closing is the real fix not the hands. Once the shoulders close back to square the athlete should stop the cue. Sadly most who try this keep cueing too long. If shoulder doesn't close you will probably see either a bailed jump, coming up short, eating top arm side standard. A good example of the open shoulder than close is Jeremy Scott. Notice open than massive arms to close than bam just working the pole to inversion. http://www.youtube.com/watch?v=HTLggEYLVko&sns=em
(video I found quick not saying his best example) (not what I personally teach)
My advice to athletes or new coaches who are designing a model to teach. Figure out what you want than find the athlete who demonstrates those movements for the vaulter to look at. To just trash vaulters cause they don't do exactly what you want doesn't help anyone but your ego. If someone is jumping higher than your athlete right or wrong they are doing something better than your athlete. Figure it out of face the fact your athlete is maxed out athletically or maxed out under your system. Progression should be seen rather its PR, average height, clearing heights on smaller poles or hip height potential. Sadly progression tends to bee seen only as height cleared.