Dumbbell Curls can be performed either two-arm, one-arm, or alternating arms.
Your shoulder muscles (deltoids) play a major role in stabilizing your shoulder joint during this movement, therefore, it is not wise to fatigue your shoulder muscles too much before performing exercises of this nature. You may find the article Gym Workout Routine Rules-of-Thumb a useful reference for exercise order suggestions.
Remember, during Dumbbell Curls your shoulder joint should remain near motionless - movement occurs around your elbow joint - so do not swing a weight in order to lift more, as you'll only be cheating yourself.
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