Lie on your right side with your legs stretched out straight and stacked one on top of each other. Anchor your right arm against your right leg and the floor.
Bend your left arm at the elbow and spread the fingers of your hand to hold the very top of the back of your head.
Flex your abdominal muscles and in one motion bring your left arm and head, as well as your left leg, off the mat.
Lift your torso and your still straight left leg further off the ground. Squeeze them as closely together as you can, so that your left elbow and left leg almost touch.
Release the side jackknife by returning your torso, head and leg back to the floor in a slow, controlled movement.
Repeat this exercise about 7 more times on your left leg.
Reverse the side jackknives by turning over onto your left side with your right leg on top of your left. Bend your right arm and use your right hand to hold your head steady.
Tighten your abdominal muscles and lift your head, supported by the right arm, and your right leg off the mat.
Continue lifting to bring your right elbow and the knee of your straight right knee as close together as you can get them.
Return your right leg and torso to their original position on the mat. Do 7 more side jackknives.
Do more sets of the exercise as your strength and endurance dictate. You can add sets as your muscles strengthen to continue the workout.