[header] How to do the pilates jackknife move [title] Lie down on your back on the pilates mat with your legs straight and together. [title] Keeping your arms right beside your body with your palms facing down, raise your legs up to a 90-degree angle without bending them. [title] Exhale as you lift your hips off of the mat and curl your abs in. 
[step] Keep maintaining the 90-degree angle of your hips and legs. You'll know when you've completed this step once your knees are directly above your nose and your legs are straightened parallel to the mat.