This movement will prevent use of momentum and recruitment of the deltoids (as opposed to the traditional standing curl).
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Lie on an incline bench at around 45 degrees. Grasp a pair of dumbells.
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Let your arms hang to the sides. Your palms should be facing each other.
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Curl both dumbells towards the shoulders. As the weight moves upwards, twist your wrists such that your palms are facing your torso at the top of the movement.
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Slowly lower the dumbells, under control.
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Keep your elbows tucked in at all times, and don't use momentum.
You can also perform this exercise with a hammer grip (palms always facing each other), and/or with an alternating motion (one arm at a time).