The American Council on Exercise notes that concentration curls may be the best exercise for building the biceps as it isolates the bicep muscle more than other common exercises such as cable curls, barbell curls, chin-ups, EZ curls, incline curls, and preacher curls. To perform a concentration curl, sit with the upper arm pressed against the inside of the thigh, slowly raising and lowering the weight. American Council on Exercise, January 2023