Hold a dumbbell in each hand by your side with your palms facing inwards. Do not relax your muscles. Exhale and raise your shoulders as high as you can, then lower them back down and repeat. Make a pause at the top position of the movement. Do not relax your muscles at the bottom position, it may lead to an injury.
Mistakes and Recommendations:
Do not rotate the shoulder joints.
Do not work with your biceps. The arms always remain straight in the elbows.
Avoid jerking. Your movements must be smooth and absolutely controlled.
Keep your back straight.
Do not turn your neck or hang your head.