Interestingly the jack knife has the added advantage of hitting your lower abs a lot more than traditional sit-ups, making it a great way of adding some variety to your core routine.
CROSSFIT: WHEN EXERCISE GETS SERIOUS
The Jack Knife can be performed on the floor, a bosu ball or on a bench. In fact if you workout outdoors or in a park you can even use a park bench or a wall! The traditional jack knife is performed lying on the floor with your arms above your head and legs extended. You bend at the waist bringing your arms and torso up at the same time, raising and then lowering. However, many popular jack knife exercise use modified actions such as the one shown below.
DOES PERSONAL TRAINING REALLY WORK?
Sit on the bench with your bottom at the edge of the bench and your legs stretched out straight, your legs and feet together. Now pull your knees in toward your chest and as you do so bring your arms forward and try to touch the side of your feet. Then bring your arms back to your chest and push your legs back out straight. The slower you do this the harder it is. If you find this too difficult you can start by keeping your hands behind you on the bench. As your core strength improves you will find your balance does too. If you find it getting too easy try gripping a weight between your feet! This is a killer.
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