What specifically is built up using medicine balls for soccer? What exercises can build up core strength for soccer?
Here's a video that really outlines a lot of the exercises that will help. I have done some of them myself to condition for being a keeper. These all should be of great help to gaining core strength. http://www.youtube.com/watch?v=5ZZMcIo6-A8
For some more specifics, here are some of the ones that I trained with and found to be most beneficial:
Lie on your back with your legs straight. Use both hands to hold a medicine ball above your head and barely off the floor. Simultaneously raise your torso and bend your right knee toward your chest as you bring the ball over your knee and toward your foot. Reverse the movement and repeat, this time bending your left knee.
Do a normal crunch, but hold the medicine ball behind your head and hold it above the ground.
Doing a normal crunch, but simultaneously throwing the medicine ball to a person standing at your feet. Then, have them toss the ball back and lay back flat. I usually did this with a teammate at our practices every day for about 20 reps. I can attest to its effectiveness in giving me more strength for throws and dives as I am a keeper.
One of the best ones I found: Hold your legs straight up in the air and a medicine ball behind your head. Reach for your feet with the ball and reach back.
I would also do about 15 throw ins with the medicine ball, then 15 with a normal game ball and repeat this a couple times. I found it to really increase my accuracy and distance when throwing in. It may be extremely helpful depending on your position.
Here is a link to a sight containing other exercises, but these four were the ones I would do the most. http://www.menshealth.com/fitness/ultimate-medicine-ball-workout?fullpage=true Hope this gives you a better, more accurate idea of what helps with building core strength.
We had a fitness coach from Derby County speak to us at work and he said that he got the players core fitness and balance to improve by throwing a medicine ball to each other while sitting and balancing on a exercise ball (the big blow up types). He said at first they would practice balancing and after a week or 2 introduced the ball. Apparently they got very proficient and became quite a fiercely competitive game with harder and harder throwing which just shows how much this would have worked! Just balancing and sitting on an exercise ball requires good core strength but also throwing a heavy medicine ball at the same time is on another level.