An isolation version of the exercise for arms. Rotating your wrists allows to work biceps to the maximum, and involves all muscle fibers.
Stand up straight with your feet shoulder width apart.
Grasp the dumbbells with a parallel grip.
Your arms should be approximately shoulder width apart with your elbows slightly bent.
From the starting position, as you exhale, lift the dumbbells up slowly without moving or swinging your body.
While lifting them up, rotate your wrists so your palms shift from the parallel position to the bottom position (your palms should face each other).
Do not pause at the top, return to the starting position as you inhale.
Don't forget about a warm up.
During the exercise the emphasis is on the ligaments, so increase the weight very slowly.
In the starting position do not straighten your arms completely.