The Flaw: Going too heavy. The Fix: This may seem obvious, like the ultimate curling cliché, but it bears repeating. Too many guys go too heavy on barbell curls, with no shirt-stretching gains to show for it. Strict sets of light-moderate-weight curls can and will add size to your arms. Take the 45-pound plates off the bar and try some 10’s instead. The Fix: When curling, the forearms will be moving up and down, of course, but the upper arms should remain stationary — not moving forward or backward.