Ian,
i have no idea what a straight arm press up is - can you enlighten me please.
In a normal press-up, you lay flat in the floor, face down and use bent arms by your sides to lift your torso off the ground. Easily done by most people.
However, try laying flat in the floor, face down with both arms stretched straight out in front of you i.e. "over" your head, palms down in contact with the floor about 18in apart.
Now push down on the floor without bending your arms (no use of knees allowed) and try to lift your body off the ground so that your torso comes off the ground with only toes and hands touching the floor.
I know, I know... its near impossible (unless you have the upper body strength of a weightlifter and the body weight of a feather duster). The reason for this is that the strongest muscles in the arm, the biceps and triceps are completely taken out of the picture, and the main arm muscles in play are the deltoid & rotator cuff muscles of the shoulder and the extensor and flexor muscles of the forearm, none if which are very effective in applying transverse forces.
It demonstrates (for non believers) that it really is nearly impossible for a prop forward with their "bind" arm fully outstretched, to apply downwards, sideways or upwards force on their opponent. Transverse forces are much, much harder to apply with a straight arm than with a bent arm.
If props are made to bind with their bind arms straighter, the only real strength they do have is the ability to contract their arm, and that pulls the opposing prop toward them. If both props THP and LHP on both sides have long binds, pulling their opponent toward them, this helps to lock the scrum and keep it up.
If props are prevented from binding with bent arms, their ability to apply transverse forces to their opponent is severely minimised , they cannot pull their opponent down, nor drive him up, and nor can they twist their opponent and drive him sideways to enable boring in.
