strengthening core for walkovers necessary?

I have got two question about limber and walkover.

At the gym, there are a few teenage girls (age 12-22) starting to learn walkovers and limbers. They are all very flexible and can do good handstands and even press handstands.

1. What should I make them do to strengthen their core to not get injured on the walkovers and limber? I make sure their technique is fine of course! Do I need additional work? Hollow Rocks and Arch Rocks in High numbers? or reverse sit-ups with weights? 

2. They say that working walkovers, limbers and kick overs make their shoulder very tired and they are not able to press to handstand after about 20 minutes of limber work. Can this be true?

Thank You!

katlinchen said:

... They say that working walkovers, limbers and kick overs make their shoulder very tired and they are not able to press to handstand after about 20 minutes of limber work. Can this be true? ...

If they are weak, yes.

Yours in Fitness,

Coach Sommer