One arm pinned, zero swing, full peak.
Keep the back of your arm glued to the pad, don't let the elbow lift to cheat.
Running the preacher pad one arm at a time pins your upper arm so the dumbbell can only move by the biceps flexing the elbow, and working one side at a time means your stronger arm cannot quietly bail out the weaker one. The pad angle bites hardest near the stretched bottom of the rep. It is the go-to for evening out arm imbalances while keeping every rep strict.
Each arm works alone, so imbalances get exposed and fixed rather than hidden. You can also adjust your position slightly per arm for a perfect pad fit, which a bar never allows.
Lead with your weaker arm and let it set the rep count, then match that number with the stronger side. That stops the gap growing set after set.
Yes, once the elbow rises the shoulder starts helping and the isolation is gone. End the rep just before the elbow wants to lift, and keep the back of the arm glued down.
