How to do the Jack KnivesThis exercise can be performed with your knees bent or kept straight. Lie on the ground (beginner) or a bench (advanced) with your lower body not on the bench. Complete a crunch and bring your knees and shoulders together. This exercise takes a lot of balance and is great for any athletes.
Note: If you feel you are starting to lose your balance, put your foot down. A bench allows for more stabilizer muscles to be activated to maintain your balance.
These are the muscles , equipment and categories of this exercise.
- PRIMARY: Abdominal
- Lower Abdominal
- Hip Flexors
Averages for MyFit UsersThe table below represents data from over 200,000 exercise logs and gives us an average for this exercise.
|Average Weight Lifted||Average Reps||One Rep Max Average|
|10.6 lbs||16.7||20.7 lbs|
What is a good starting weight?
Based on an average weight lifted of 10.6 lbs for all MyFit users we suggest you start at 50% of that weight: