Like an LBD, great abs never go out of style. And if there’s one person who’s got them, it’s Astrid Swan, the Los Angeles-based personal trainer behind Julianne Hough‘s dancer bod. She shared with us nine equipment-free exercises that can take as little as 20 minutes and are guaranteed to tone your core. Says Swan, “I love to have my clients do these ab moves, because they work the entire core while also getting the heart rate up and can be done anywhere at any time! We can do this as a burn out at the end of a workout or on its own before hitting the pool.” Get ready to be ab-solutely strong.

1. Deconstructed Jackknife: Start laying on your back, and V-up to a top jackknife position, hands reaching for toes, balancing on your sit bone. Hold for a moment. Move your arms back behind your head and hold another moment before opening your body up. Hover at your lowest range before lying all the way flat. Be sure to keep your spine pressed down and abs pulled in. Repeat slowly 10 reps.

2. Figure 4 Jack Legs: Start laying on your back with your right leg extended straight on the floor, then cross your left foot over your right knee to make a “figure 4” position. Lift your shoulders, upper back, and head up to a crunch, and hold that crunch. Raise and lower the figure 4 slowly for 15 reps, and then repeat on the other side.

3. Windshield Wiper Plank: Start in a plank, lift your right leg up two inches from the floor, and sweep the leg over to the side as far as you can without the hips moving. Return the leg back to starting plank, and repeat on the other side. Do 20 reps.

4. Diamond Knock-Knee Crunch: Laying on your back with your knees open to a diamond shape and soles of the feet touching, crunch up so your elbows and knees touch. Rest your crunch and change your diamond position to knees touching and feet separated to the sides, and crunch again. Keep switching the diamond shape. Do 20 reps.

5. V-Sit Scissor: Balancing on your sit bone in a V-sit position, scissor your legs and, with straight arms, chop one arm over the top leg while the other arm stretches behind. Do 40 reps (20 per side). Modification: Bend your knees.

6. Side V-Up: Laying on your right side, extend your right arm out, and bring your left hand behind the head. Lift your legs and shoulder up into a side V-sit. Lay all the way flat each rep. Do 20 reps. Repeat on the other side.

7. Side Hallow Hold: Laying on your side, extend your arms straight out, “glue” your arms to your ears, lift up as high as you can, and then lift up the legs. Hold this position for 20 seconds, and repeat on the other side.

8. Stomach Swivel: Start laying on your stomach with your arms by your side. Lift up your chest from the floor, but keep your chin tucked. Swivel side to side, trying to get your fingertips to reach for the outside of your knees. Be sure to keep your hips tucked and squeeze the glutes as well.

9. Plié Twist: Starting in a plié position. Squat low with your hands behind your head. Staying low, stretch over side to side so the elbow touches the center quad, and return sharp to the starting position. Do 40 reps (20 per side).

What are your favorite ab exercises? Share them with us @BritandCo!

(Photos and GIFs via Astrid Swan)