some thing I don't understand in video

i don’t understand very well english (speak).
so I want to ask some thing idon’t understand (and don’t open 1000 thread on thing I don’t know).

warm up: stretch is done to achieve normal ROM, but PNF is done “Strong” in the video…normally in the warm up I must do Light stretching, both for dinamic, static and PNF.(don’t force?). is different if I’m tigh or not?

Addominal work
both in high and low intensity? 50 reps in high and don’t understand in low, but understand it must be done whit extensive excersise.
and i don’t understand the question about abdominal work and hip extension.

In the PNF example, there is no forcing of a stretch and the push back is regulated by the athlete’s readiness. The less force the athlete exerts, it is likely the tighter that athlete is and therefore the more repetitions of the stretch are performaed- but always the force and range of motion is controlled by the athlete.