Stress.

[greynotsoold]

I think that if you are feeling tension you are doing it wrong; the only moment of being tight is just before impact.
I think that there is too much of a 'no pain no gain' mentality. If you hurt you are doing it wrong.

Funny enough Greys the last 15% of movement, is how we are designed to work. to our optimum.

I'm not sure I understand what you mean there.