Jackknife exercise is a great exercise for focusing on the rectus abdominis and transverse abdominis which form the outer and inner core of the abdominal muscle.

Jackknifes generates an intense contraction at the top position but also engages the hip flexors upon extension of the legs as well as creates a nice stretch on the lower back and hips.

Jackknife can be used as a warm up to prime the hip flexors and lower back before training your back or legs or as a finisher in an abdominal workout routine.

Jackknifes Exercise How To

  • Lie on your back then fully extend your arms and legs. Keep them off the floor throughout the duration of the exercise.
  • Contract your hip flexors, bend your knees and bring them toward your abdominal area. Simultaneously bring your arms up and forward, past your knees. Your shoulders should come off the floor. Hold the position for a count of “one”.
  • Simultaneously extend your hip flexors to straighten the legs and lower your torso back to starting position. Make sure your arms are back to their fully extended position behind your head.
  • Another variation is to simultaneously bring your fully extended legs and arms together at the top position. Hold the position for a count of “one”.
  • Bring your arms and legs back to starting position by resisting your bodyweight.
  • Repeat the exercise until you have completed the targeted number of reps.

Form and Technique

You get great results from Jackknife by maintaining constant tension throughout the exercise.

This is why you should not let your feet and shoulders rest on the floor at the bottom part of the exercise.

Focus on contracting the abs and hip flexors and getting a good extension and stretch at the bottom part of Jackknife.

Do not use momentum to bring your legs off the floor.

Variations: Jackknife Crunch, Swiss Ball Jackknife, V Up

Routine for Strength: 5 sets x AMRAP (30 secs rest between sets)

Routine for Muscle Gains: n/a


How To Do Jackknife