Criss-cross crunches will work the hardest-to-target muscles in your core

If your harder-to-hit core muscles had a campaign slogan, it would be “stronger together.”

Allow me to explain. Instead of working each of the 12-ish muscles that make up your trunk on their own, you’ll get better results when you work them together, particularly when it comes to strengthening those harder-to-target muscles (like the lower abs and the obliques). “When we use the body as a system instead of through isolation movements, we are able to really maximize the potential of our strength,” says Obé fitness trainer Emily Diers. This is particularly applicable to your core workouts, since incorporating numerous muscles at once makes your moves more effective.

Sweating through combo ab moves is helpful in getting to spots like your adductors, lower abs, and obliques, which are hard to hit on their own in isolated exercises to begin with. “When we use our adductors and obliques together, they form a really powerful team to streamline our strength at the midline of the body,” she says. “Our adductor muscles help to draw the legs closer to the midline and flex at the hip, and our obliques help with rotation of the trunk.” When you do combo movements targeting all of them, it’ll stabilize your pelvis, improve your core rotation, and of course, strengthen your muscles.

Below, Diers shares three go-to combo moves that’ll have your entire core quaking… and feeling stronger together, for sure.

Lower ab and oblique workout

1.Elbow to knee: Start with your legs straight on the floor with your heels in line with your hips and hands behind your head. Keeping your hips facing the ceiling, curl up and twist to bring your opposite elbow to knee, feeling the contraction in your obliques and flexion at your hips. Repeat eight times.

2. Knee squeeze: Starting in the same position, hold your right elbow to your left knee. Bring your right knee up to squeeze behind the left knee. “This is where the adduction comes into play and obliques have to really stabilize the twist in the core,” says Diers. “Because your pelvis is stabilized here, your low abs can easily help lift the bottom leg.” Keep holding the twist as you put your right leg down, then lower your spine and lengthen your leg. Repeat eight times.

3.  Squeeze and lengthen: Starting in the same cross-legged position, hold the contraction of your right elbow to your left knee to target the obliques. Squeeze your right knee behind the left and lengthen it out without releasing the twist. Repeat eight times.

To add some arms to your sweat sesh, try this equipment-free arm workout. And don’t forget to go through a full-body stretch—using one of our favorite stretches—when you’re done.