Jackknife Exercise Works Your Lower Core Like Nothing Else

When your fitness instructor cues jackknife exercise (also known as a “V-up”), you know you’re in trouble. This abs-centric move requires full-body engagement and is a favorite of Pilates, yoga, HIIT, and strength training classes alike. Jackknives also happen to be one of the most technically challenging core exercises out there. If you’re not quite sure that you’ve achieved A+ form yet, never fear.

“[Jackknives] a great move for your core, especially your lower abs and your hip flexors,” says Nike master trainer Traci Copeland, your jackknife guide for this week’s episode of Well+Good’s The Right Way. The move also challenges your upper body and back strength because you have to bring your trunk to meet your lower body—no small feat.

Never heard of a jackknife? Here’s how it goes: Lie down and fully extend your arms overhead. Using your lower core, sink your tailbone under and, keeping your back as straight as possible, lift your legs and upper body off the ground, reaching your hands to your ankles so your body forms a V-shape. (You can also keep your legs bent, if this feels better.) Next, bring your legs and your upper body down to hover just above the floor, making sure to keep your abs fully engaged. Come back up into your V-shape and keep repeating until you’ve completed the necessary reps. Watch Copeland demo each step to make sure you’re practicing proper form.

Sounds simple enough—but in practice, it’s a little tricky. Like any fitness move, the jackknife requires plenty of practice, and Copeland says the folks in her classes tend to make the same few mistakes again and again. First, people tend to arch their back in this exercise, a common mistake in abs exercises that puts your lower back in jeopardy.

And second, it’s really tempting to rely on momentum to execute your jackknife, but the magic of this move actually lies in staying in control and holding at the top, says Copeland. (Of course, it’s way harder this way, but are you really surprised?)

Now that you know the ins and outs of the jackknife exercise, you’re ready to take HIIT class by storm. Just keep your two cues in mind: Core engaged! No momentum!

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