Want to eliminate upper arm jiggle and wave hello with confidence once again? You can, with this upper body exercise for slimmer arms.

This simple-but-challenging move is totally worth it, whether you want arms like Jessica Biel’s, stronger shoulders, or a little more flex in your biceps.

In this video, fitness and health expert, Cynthia Sass, RD, shows you how to do the thumb arm figure 8. Stand with your arms out and thumbs up. Then tip your thumbs down and back to begin tracing a figure 8. At the bottom of the circle, turn thumbs up and continute. Trace the rest of the figure 8, ending with your thumbs up.

This sequence is one rep. Sass recommends doing 50 reps.

For added difficulty, hold a 3-pound dumbbell in each hand while doing the figure 8.