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Jack Knife Sit-Ups

An oldie but a goodie, jackknife sit-ups can add an extra dimension to your abdominal workout. They can be performed with or without weights, in a face-up or prone position, and with or without resistance bands.  A classic exercise that has endured the test of time, jackknife sit-ups or V-ups may be just what you are looking for to carve out and finely sculpt that six-pack you’ve been working so hard to achieve.

So what exactly is a jackknife sit-up? Consider the jackknife; a compact device that unfolds into a multi-faceted toolset. Jackknife sit-ups get their name from the pocket knife of the same moniker – from a compressed position you unfold your body, and then compress it again.  Also known as V-Ups, this abdominal exercise works all the quadrants of the abdomen and done correctly, requires extraordinary focus and strength to isolate the muscles of the torso.

Begin In Jackknife Position

Before we talk about weights, resistance bands, balls or other accessories that you can you to enhance V-Ups, let’s start at the beginning. Laying on your back, extend your legs fully and reach your arms over your head. Now pull your shoulders away from your ears, keeping your arms extended. This helps isolate and contract the abdominal. Now exhale and pull your navel to your spine, keeping your abdominals contracted.  From this position, lift your torso and legs using only your abs.

At first, you may only get your legs and torso a few inches off the ground.  That’s ok. It means you’re doing it correctly! Release back to the floor and do it again, focusing on using your abs to lift your legs and torso. When you start engaging your hip flexors and using your neck and shoulders for lift, you aren’t doing the exercise correctly and you may injure yourself.

Practice makes perfect, so keep trying. These V-ups build strength quickly, so before long you’ll have great form and be able to switch things up a bit.

Enhancing Jackknife Sit-Ups

These abdominals exercise can be frustrating, so one way to get the full benefit without the hassle is to use an inflated ball.  In plank position, place the top of the ball at your shins and flex your feet over the end of the ball to stabilize it. Using your abdominals, begin to lift your hips to the ceiling, keeping the ball glued to your shins, and coming into an upside-down jackknife position. Lower your hips and roll the ball back the starting position. Repeat until muscle fatigue.

You can also perform a modified V-up using a resistance band. This version is great if you are injured or want to isolate the obliques and sides of your abdominals a bit more.

Wrap a resistance band around one foot and extend your legs. Holding the other end of the band with your hand, begin to lean your torso back toward the floor, raising the leg that has the resistance band around it. When you are in an upright V position begin to lower your leg to the ground which extending your arm back toward the wall behind you.  From this position open and close as if you were folding a tool back into a jackknife.  Repeat to muscle failure and then repeat on the other side.

Weighted Crunches (Or Sit-Ups)

The real difference between sit-up and crunches is that a sit-up is a full range of motion exercise, and a crunch is basically a half sit-up.  Whichever exercise you prefer, be sure to fully engage your core by tucking your tailbone and pulling your belly button back toward your spine.  Using only your abdominal muscles, lift your torso off the floor.

You can make this exercise more challenging by holding a weight on your chest to add resistance. It’s important to take care of your neck by keeping your chin tucked, particularly if you are performing weighted crunches, so you don’t strain the muscles of your neck or your traps. Whenever you feel the tension move away from your abs and into your neck, shoulder or hips it’s time to stop and take a break.

Abdominal exercises only work effectively if you are using your abs exclusively and not engaging other muscles for momentum or assistance.

Jackknife sit-ups can also be performed by contracting or crunching from side to side, rather than contracting toward the midline of your body. These “side jackknives” work the oblique muscles and can help with strength and definition in the harder to isolate areas of the torso.


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