Which is harder, a seated dumbbell curl or a standing one

Level 4: You use minimal stability support for the curl (or any practical exercise) this means try a curl standing on only one foot.

Level 5: This is very, very difficult; but possible. You use no stabalizing support (don't try this until you have successfully managed Level 4 and you have a spotter, ease up to this level, it can become dangerous to you or people around you.) This means sit on a ball using no body part touching any solid surface including the ground, (you've probably seen the large stability balls in many gyms.)

Remember these levels apply to all practical exercises. Use them in the correct sequence and only use the lowest level you are comfortable with. It is always important to have a spotter.

And like peachtool was saying isolate the curl and don't 'ROCK' your body to 'cheat' the curl. ~HAVE FUN~ -o