Straight or EZ bar: Which is best for building biceps?

Although the EZ bar (a shorter bar found in many gyms with "bends" where you grip it) is often used when people train their biceps, researchers from Oklahoma State University have shown that a straight bar actually produces greater muscle activity in the biceps. Although one of the main roles of the biceps is to flex the elbow joint, it also rotates the palm. In other words, if you hold your palm face down, then twist it so that it faces up, the biceps is doing some of the work.
With a straight bar, the palm is already facing up. With the EZ bar, your palms are angled in slightly so they face each other. The researchers think this is one reason why the EZ bar curl reduces muscle activity in the biceps compared to using a straight bar.
Of course, the EZ bar does work other muscles well, such as the forearmsand side of the upper arm. However, if you want to get maximum growth of the biceps, make sure that the straight barbell curl is used. Dumbbell curls with the palms facing up for the whole movement are also be highly effective for this purpose.