How To Do The Jackknife Crunch Properly

The jackknife crunch is a strengthening exercise tailored to engage the abdominal area and subsequently increase strength levels within the area.

What the jackknife does is it directs strain towards the muscles in the anterior abdominal walls, Consequently, this leads to the burning of calories within and around this area which then lowers the body fat especially around the rectus abdominis area.

A low-fat rectus abdominis (abs) exposes the ribbed structure of said muscle which is what is found culturally aesthetically pleasing and to some considered the ultimate form of fitness.


  • Lie flat on an exercise mat or a comfortable piece of clothing, such as the towel. Extend your arms straight back behind your head. Ensure your legs are fully extended and this is your starting position.
  • Bend at your waist and raise your legs and arms to meet in a closed jackknife position.
  • Ensure your legs are still fully extended at 35–45-degree angle from the floor
  • Your arms should also be extended, in a position that’s parallel to your legs.
  • Raise your upper body from the floor
  • Return to the start position by lowering your arms and legs back to the floor, exhale as you do so.



One of the major areas that the jackknife crunch engages is the core. The core is responsible for playing a part in the majority of movements throughout the jackknife crunch

This ranges from acting as a pivot to facilitate your elevation to controlling your momentum as you go up and down.

All these movements and actions direct strain the core and train the area into becoming stronger


The upper and lower abdominal muscles are made up of a number of tiny cogs such as the rectus abdominis, external oblique, and the transversus abdominis.

All these areas are engaged by the jackknife crunch in various capacities whether its regulation of momentum, providing balance mid-movement or facilitating elevation.

In the end, this results in the tightening of said abdominal muscles which helps them perform their roles better i.e., holding the internal organs in place.


While doing the jackknife crunch, the glutes work in conjunction with the hip flexors to help with elevation and balance during movements.

The glutes are particularly important when it comes to balance. This is because as you hang mid-air, the glutes help with the pull of gravity to ensure that your movements are maintained within the central body plane.


The lower back is another pivotal muscle when it comes to balance while doing the jackknife crunch.

The lower back is largely made up of the erector spinae and closely works with the glutes. It also works with the abominable muscles to make the primary movements – bending and flexing possible.

However, it’s most engaged when you hang mid-air and are forced to balance your momentum when you lower yourself.



Although the largest magnitude of focus is directed to the lower and upper abdominal muscles, the core area is pretty much the area that benefits from the strengthening.

This is because as an exercise, the jackknife crunch engages almost all of the core areas. The core is primarily made up of the back extensors, the trunk area and the hip muscles.

All these areas are engaged in various phases of the exercise’s movements.


The amount of work that the back, especially the lower back is put through forces the area to grow stronger. This is because the more you force your body to handle the strain from the exercise the more it adapts.

As a result, it leads to a stronger back which is beneficial even in the long term. A strong back puts you in a better position to avoid back injuries.


One of the most difficult areas to burn fat off is the abdominal area especially if its subcutaneous fat.

However, the jackknife crunch provides the ability to burn fat off the difficult areas to get to i.e., the transverse abdominis area.



  • Stand with your feet hip-width apart and stretch your arms above your head while you hold your hands together.
  • Rotate your torso to face the right side of the room, making sure your feet and hips stay forward.
  • Lower your torso down to the right then toward your toes as you try to keep your legs straight.


Although the child’s pose exercise is based on a yoga-like outlook it has numerous physical benefits as well, similar to the jackknife crunch.


  • Lower yourself to your hands and knees on a comfortable surface i.e., a matt or towel
  • Spread your knees as far wide as the width of the surface material and ensure the tops of your feet are touching the ground.
  • Ensure your belly lies between your thighs and plant your forehead on the floor in a comfortable position.
  • Relax your shoulders
  • Stretch your arms in front of you with your palms toward the floor
  • Stay in this position for about 30 seconds and start again.


  • Lie on your right side with your legs straight and feet stacked on top of each other.
  • Place your right elbow under your right shoulder with your forearm pointing away from you and your hand balled into a fist.
  • Ensure your neck is neutral, breathe out and brace your core.
  • Lift your hips off the ground and push your body’s weight onto your elbow and the side of your right foot.
  • Hold this position for the duration of the exercise.
  • Depending on your fitness level, aim for between 15 to 60 seconds. Repeat on your left side.



By pushing your neck up with your hands, you take away the strain that is meant to be directed towards the core and other engaged areas.

This also places your neck in an awkward position which can easily lead to a neck or spinal injury.


Momentum is a common way of reducing strain while doing an exercise. This is because it reduces the amount of time that you engage the target muscles.

Consequently, it ends up watering down the effect of your exercise which reduces efficiency.


The jackknife crunch is a really simple exercise that will get to those deep recesses of fat that you seek to burn.

Be prepared for that burn afterward though because it is a thoroughly engaging exercise.