If you want to define your waist and strengthen your core, you’ll need more than straight sit-ups to make a measurable difference.

To feel firmer in five minutes, try this quick fix from NYC-based certified fitness trainer Chris Sams, modeled by Instagram star Yovanna Ventura. For each exercise, do as many reps as you can in 30 to 60 seconds, switching sides when necessary halfway through. Then then move onto the next exercise.

1. Thread the Needle

How to do it: Get into plank position with your shoulders stacked over your wrists and your body in a straight line between the top of your head and your heels. Keeping your hips squared to the ground, bring your right knee to your right elbow. Next, extend the right leg across your body and under your left leg. Bring the right knee back to the right elbow to complete one rep.

2. Forearm Plank Swimmers

How to do it: Get into a forearm plank with your shoulders stacked over your elbows and palms pressed against the ground. Extend your right arm straight out in front of you, then open it out to the side before returning to plank position. Repeat on the opposite side and continue to alternate sides.

3. Leg Crossovers

How to do it: Lie face-up on a mat with your palms pressed against the ground beneath your hips for support and legs extended. Keeping your lower back against the ground, lift both legs about a foot off the ground. Keeping the legs as straight as possible, cross the left ankle over the right one. Then reverse, crossing the right ankle over the left one.

4. Side Plank With Twist

How to do it: Get into a side plank position on a mat with your left forearm on the floor, left fingertips facing the right side of your mat. Your shoulders, hips, and feet should be stacked, but you can stagger your feet to make this move easier. Without dropping your hips, use your right arm to reach underneath the body. Next, open the chest and reach your right arm straight up overhead. That’s one rep.

5. Russian Twists

How to do it: Grab a 5- to 10-pound dumbbell in both hands and hold it at chest level. Sit on your butt with bent knees and crossed ankles. Lean backward slightly to lift both feet off the ground. Keeping your shoulders away from your ears, twist from the waist to turn your upper body to the left. Repeat on the opposite side and continue to alternate without dropping your feet.