Sit on the end of one flat bench, hang your two arms down the side of your torso，elbows close to your torso, hold one dumbbell in each hand, palms facing each other. That is your starting position
Keep your upper arms stationary and elbows close to your torso. Contract your biceps to curl two dumbbells up-out and rotate your palms together until dumbbells reach your shoulders’ height， palms become to face up and forearms are in line with your outer deltoids, hold the position for two seconds as you squeeze your biceps
Then, slowly lower the dumbbells back and rotate your palms together to the starting position
Breathe out when raising and in when lowering
Keep your upper body stationary during the whole process, and do not jerk your upper body to help you raise the dumbbells
Keep your elbows close to your torso, and only the forearms could move
When you raise the dumbbells at the top of the movement. For the peak contraction, your small fingers should be higher than your thumb and your forearms should be in line with your outer deltoids.