I’ve put in a lot of work recently in order to get my arms stronger (you know, so that I can carry my 21-pound puppy who sometimes refuses to walk). Usually, I’ll turn to a resistance bands arm workout, knock out some push-ups, or hit up the weights and do bicep curls/tricep work/hammer curls/chest presses/etc. Then, while streaming a Peloton strength training workout the other day, I was instructed to do something called a “halo,” and every single muscle in my arms is still sore.

Don’t be fooled by its innocent-sounding name—there is absolutely nothing angelic about it. Watching someone else do it, you might think, “eh—it’s not that bad.” Or at least, I did. But when I grabbed a weight and tried it myself, I quickly realized it was a serious feat of strength (especially after three rounds interspersed with push-ups and other moves). To give you an idea, the halo involves taking a weight—a heavy one, might I add—and beginning by holding it horizontally in front of your chest, then rotating it by your left ear, behind your head, then to the right side of your head, and back to your chest. Then switching directions.

“Halos are a great stability exercise for the core,” says Tatiana Lampa, a trainer with Fithouse. “It’s also a great shoulder exercise.” Well, and your full arms… because I can still barely lift mine. She notes that you can use either a kettle bell or a dumbbell in a moderate weight. “But it feels nicer on the hands to hold a kettlebell,” says Lampa.

Her pro tips? “Start with your legs hip-width, hips tucked under by squeezing the glutes with no arch of the low back,” she says. “Keep your abs super tight. Your elbows must frame the forehead to start, then as you bring the kettlebell behind your head, you must not be able to see the kettlebell when it’s behind you.” Then do it on the other side—just make sure your body stays completely squared without moving your core or your hips. Knock out a few sets of, say, 30-second intervals, and you’ll definitely feel the burn. Just ask my triceps.