Spider curls are a challenging and safe way to target your biceps while also preventing some common pitfalls. Here's what the exercise looks like:

Spider curls reinforce proper elbow flexion mechanics through a dead hang and vertical position of both arms. This downward pull of gravity makes it extremely difficult to draw the shoulder upward into flexion, a technique mistake made by many lifters.

Spider curls teach you not to substitute the anterior delts for training your biceps. You want to focus on moving the biceps dynamically; the shoulders should serve only as stabilizers. Once you master the awkward initial setup position, it's just hard to do spider curls wrong.

The spider curl really nails the short head of the biceps throughout the entire range of motion, especially the top of the movement where you can normally "rest" and lose tension.

This type of curl also has a lot of carryover to other biceps exercises. It'll help ensure a proper finish position to maximize time under tension.

Last but not least, the nature of the setup removes the potential for other joints, such as your hips, knees, and low back, to assist in the movement. It's very hard to cheat on spider curls. Give them a shot with dumbbells or a barbell.