Well, maybe not rock hard. But nice. emotion_awesome
this works for me, but i'm a 5'4 Brasilian who plays volleyball for about 5 hours a week, so... Maybe it'll work for you, maybe not.
Because in volleyball you don't really get the tummy, but more the arms and legs toned, I asked my coach what would be good for abs, because I'm very self conscious about my bellyfat x)
She told me a bunch of things, varying around a bajillion reps of squats, etc.. but I have a fifteen minute ab exercise. (for guys, you could probably just double it. so when i say a five minute exercise, just assume i mean 10.)
You can do it anytime, but I like to do it at night before i take a shower/go to bed. Start off with just doing five minutesworth of a plank. A plank is like when you're doing a push up, except your hands are folded ( http://img4.cookinglight.com/i/2009/03/0903p52a-plank-l.jpg?400:400 ) this helps in toning your shoulders and your abs. This is the hardest part.
Then do five minutesworth of sit ups. You can do orthodox sit ups, or unorthodox. I like to do a mix of orthodox and unorthodox, but pick your pleasure.
Then, my favorite part, drink green tea. Seriously, the stuff boosts metabolism like a horse eats hay. And yoga's really good too, but i'm not going to teach you how to do yoga! Go youtube it. biggrin
And help me with my quests!
Kony 2012 http://youtu.be/Y4MnpzG5Sqc
Gaia quest http://tektek.org/avatar/48491194