Body control training -- stay close to the bottom by keeping your knees tight against your body, and your trunk stable.

http://en.wikipedia.org/wiki/Mammalian_diving_reflex

Hanging out on the bottom can be a dangerous excercise for two reasons. Please take these precautions:

#1. Don't let anyone jump in the pool while someone is doing this drill. Educate the athletes about safety. The responsibility is one THE PERSON WHO IS UNDERWATER to communicate to others about what they are doing. Even if there is no one diving in, the person underwater must LOOK UP before getting up to the surface.

#2. This drill is not a contest to see who stays under the longest.

This drill is for body control and awareness and activating the diving reflex. As far as I can tell you can activate the diving reflex by simply putting your face under, but laying down on the bottom is very relaxing. It's a little bit easier on the front, so you might start there -- then the athlete can rotate onto their back.

Once the core is stabalized by the bar, the real work begins!

Rotating during vertical kick drills adds a specific skill challenge that carries over to free and back swimming.

Backstroke Kick with a Swiss Ball. Make sure the ahtlete does not just hold the ball -- ideally the athlete HUGS the ball pretty tight to activate the trunk.

Human stroke, hand drag, finger drag, swim: Evolution Drill

Head up Free evolving into free swim

Start with head up free, kicking well. Lower the head and drive the kick. When the athlete feels the kick give them maximum propulsion, they have found the proper spot for their head. Stay with that head position for the rest of the length.