My work at the Human Performance Lab at the University of Tampa allows me to investigate new ways to increase muscle activation through exercise. One thing I've discovered is that if you want bigger biceps, doing spider curls a different way can get you to those big peaks faster.
Spider curls are usually done off the steep side of a preacher bench, but something told me that the biceps might get more stimulation if the curls were done off the top of an incline bench. As I describe in my article on increasing lat activation, electromyography (EMG) analysis, which measures muscle activation, is a great way to measure the efficiency of different exercises. I used EMG to confirm my hunch: Making the biceps do more work in the starting position increases muscle activation.
The Power of Constant Contraction
When you do spider curls the "normal" way on a preacher bench, your upper arms hang perpendicular to the floor. This puts your biceps in a relaxed position. To really dial up the muscle activity, flex your shoulders to about 90 degrees (as if you were doing the first part of a front raise) and 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.
My tweak 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!
Gain Big Even With a Light Start
The first time you try this new starting position, be sure to use a lighter load than normal. Maintaining this new "flexed" starting position is hard! But not to worry. Even with a lighter weight, you'll be maximizing tension where it'll do the most good.
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.
Okay, there you have it. Now crush some arms!