skullcrushers on stability ball.

this will work your triceps and your core.

start buy laying on a stability ball with the ball mainly under your upper back.  make sure to hold your abs tight and keep your butt raised so your body is straight.

hold a dumbbell in each hand and put your arms straight up in the air.

bend your elbows and lower the dumbbells down to either side of your head~or your skull! hence the name ;) make sure your arms form a 90 degree angle.

repeat. i like to do 3 sets of 15 reps.