"I've done barbell curls for years, but my arms don't seem to be growing. What am I doing wrong?" — Sean H., Los Angeles, CA.
"Use less weight and a slow, steady tempo," says strength and conditiong coach Tony Bonvechio, of Cressey Sports Performance in Hudson, Massachusetts. "Squeeze your biceps as hard as possible at the top, and lower down over the course of four seconds."
Go right into the next rep—and stop one rep shy of failure each set. This keeps constant tension on the muscles and induces the fatigue you need to signal muscle growth.
For variety, try EZ-bar preacher curls, which are done with stricter form, and dumbbell curls, which let you rotate your wrists outward at the top of each rep for a fuller contraction.