"V' sit-ups

Yes and yes to a degree. Why are you questioning your coach?

Increasing stride length and frequency, along with foot contact power output increases speed.

Hip flexors are part of the chain, but already developed in most American athletes.

Focusing on the posterior chain (hip flexors are located in front of the body) muscles such as glutes and hamstrings help increase running speed and are lacking in most American youth athletes.

With that said do the V-Ups with everything you have and always listen to your coach.

Thanks for your replies.

I hope my first post did not seem as though I was "doubting" my coach, as I am not; however clearly that impression was portrayed. As I said in my original post, yet in a different context, there can often be things "lost in translation".
What you might be suprised to hear is that I have never had as good of a relationship with any other coach or teacher in my entire life as I have with this coach and the head coach.
I am just the type of person who feels he needs to hear multiple opinions to fully understand a concept that is foreign to me, and I hope I do not come across as obnoxious.

Thank you Mr. Doyle and Maxx not only for your imput but also and most importantly for helping me notice that what I ask harmlessly can potentially be interpreted negatively. The culmination of such seemingly "small" lessons is what eventually builds someone my age into a responsible adult.

Hey no problem--and I didn't want you to think I was chastising you

Like Jon, said, hip flexors are just one part of the whole equation. Personally, v-ups with legs straight are one of my favorite exercises for the abdominals. It takes a lot of strength to do a good number of quality v-ups.