Jacnifes are a core strengthening exercise that targets the obliques, rectus abdominis and also the hip flexor muscles. The upper body is also active in supporting the body. Jacnifes are a progression of both a push up and a bridge movement. Ensure you can perform both before progressing to this movement.
Jacknifes engage the core muscles along with the arms and the legs this increases the aerobic demand of the exercise. For this reason jacknifes are a good circuit exercise when looking to combine weight loss and core strengthening
Exercise Technique Tips - Swiss Ball Jacknifes
Keep hips down during the movement
Push legs and straighten knees during the extension phase