One simple tweak to your spider curl will have you shredding your sleeves this summer.
If you want bigger biceps, doing spider curls a different way can get you to those big peaks faster.
EMG is an awesome way to test how your muscles are performing. Spider curls are usually done off the steep side of a preacher bench, but you can get more stimulation if the curls were done off the top of an incline bench.
A regular spider curl puts your biceps in a relaxed position, not giving constant strain on the muscles. If you want to increase muscle activity, flex your shoulders to about 90 degrees, then start your spider curls from there.
This one change enables you to initiate the curl with the biceps already contracted, rather than relaxed. This initial contraction increases the biceps "time under tension," an important factor in muscle hypertrophy. If you start with your arms simply hanging straight down, you lose all that tension—and all those gains.
This elbows-forward position also increases the peak contraction by getting the biceps into a much shorter position than when your arms hang at your sides.
This slight change is based on the fact that your biceps brachii doesn't just enable elbow flexion. While both the short and long heads act as elbow flexors, the long head also flexes the shoulder. Starting in the new position works both the short and long heads of the biceps, so you get two gains for one exercise!
When you try this at first, like most new techniques, start out with a lower weight, then increase as your confidence does. This new position can be tough.
Spider curls are harder when you do them this way because the incline doesn't provide the same upper-arm stability you get from the preacher bench. This instability forces your muscles to engage more, which creates more muscle activation—and that means more muscle growth.