Grasp a pair of dumbbells and lie back on an incline bench set at about 60 degrees, allowing your arms to hang straight down toward the floor by your sides. Use an underhand grip, with your palms facing each other. Keeping your shoulders back and upper arms in a fixed position perpendicular to the floor, lock your elbows at your sides and curl both dumbbells toward your shoulders with your palms facing up at the top of the movement. Slowly return the dumbbells to the start position.