Chest down, biceps cooked. Zero cheating allowed.
The incline kills momentum on purpose. Don't swing, just contract.
Lying chest down on an incline bench puts your arms in front of your body and hanging straight at gravity, which means the biceps get tension from the very bottom of the curl and nowhere to hide at any point. The bench blocks the shoulder swing and body English that let heavy standing curls go soft. It is pure isolation work, ideal as the strict finisher after your heavier pulling and curling is done.
Both kill momentum, but a preacher pad supports the arm from behind while the spider curl lets it hang free below you. The spider curl tends to keep more tension at the top of the rep, so squeeze hard up there.
Because the incline removes every cheat you did not know you were using. With no hip drive or shoulder swing, the biceps carry everything, so drop the load and take the full stretch at the bottom.
With the arms in front of the body, the short head does more of the work. Pair spider curls with an incline curl, where the arms drift behind you, and you have both ends of the muscle covered.
