GQjock saidWhen you are training you need to learn a thing or two about the physiology and biomechanics of muscle movement
The biceps are a pretty simple set of muscle that bring the hand AND forearm up toward the shoulder
The forearm on the other hand
are a more complex group
with more complex motions
they mostly are responsible for movement at the wrist
and think of all the ways your wrist can move
abduction and adduction
SO... if you want to see bicep growth and not growth in the forearms
you need to keep all motion at the wrist down to Zero
I generally agree but it's not only stabilizing the wrists at zero degrees to isolate the biceps, it's also the type of grip you use. Pronation of the forearm (reverse grip) with a curl will activate the brachioradialis muscle (muscle of the upper forearm). Using a neutral posture (seen in fundamental position, basically a hammer grip) with a curl will activate the brachialis (muscle closest to the elbow on the upper arm). Supination of the forearm with a curl will activate the bicep brachii. So cspyny, you should ensure that your forearm is supinated throughout the entire range of motion and at the peak, slightly rotate the arm so that the pinky is close to your face. Have you played around with concentration curls on a preachers bench? or just standing dumbbell curls?
On a side note, I would avoid dumbbell wrist curls/extensions. It's somewhat counterintuitive to forcefully extend or flex the wrists when it can lead to carpal tunnel syndrome (compression of the median nerve). On another side note, the hand segment moves at the wrist joint with the following movements: flexion, extension, hyperextension, radial flexion/deviation, ulnar flexion/deviation, and circumduction (sorry...i'm a stickler when it comes to biomechanics :p).