I was taught that I must perform a pelvic tilt prior to performing an abdominal floor crunch. Why?
In order for your upper body to rise up off the ground you must flatten your low back, which is a posterior pelvic tilt. To clearly understand lets explore pelvic tilt definitions:
The prescription of any pelvic tilt depends firstly on the understanding of anatomical terminology. Once understood one can clearly see a posterior pelvic tilt is simply a phase of the floor crunch exercise. The rule "you must tilt first" may have been directed towards an individual situation. If the floor crunch is taught and progressed properly this cue may not be a necessary part of the exercise. A teaching cue may work for certain situations but should not be memorized as a rule!