The classic that never stops building arms.
Keep your elbows still, don't swing the weight up with your back.
With the palms forward and elbows pinned, the dumbbell curl loads the biceps through their two functions at once, bending the elbow and keeping the forearm turned up. Dumbbells let each arm work independently and move through its natural path, so a stronger side can never quietly cover for a weaker one the way a bar allows. It earns its place as the baseline arm builder every programme comes back to.
Both build the same muscle. Curling together is more time-efficient and slightly harder on the core, while alternating lets you focus on one arm and often squeeze out an extra rep or two per side. Pick one and progress it.
If your elbows drift forward or your torso rocks back, momentum is lifting the weight instead of your biceps. Pin your elbows to your sides, brace, and if you cannot stop the swing, the dumbbells are too heavy.
Heavy enough that the last few reps of a 8 to 12 rep set are a genuine fight, light enough that your elbows stay still and you control the lowering. Biceps respond to tension and stretch, not to heaving.
