Lie face down on a flat bench with a dumbbell in one hand, palm facing down. Extend your arm fully, letting it hang straight down towards the floor. Keeping your upper arm stationary, curl the dumbbell up towards your shoulder by contracting your biceps. Pause for a moment at the top, then slowly lower the dumbbell back down to the starting position. Repeat for the desired number of repetitions, then switch arms.
GIF
