Kneel down under the lengthened TRX straps and place your feet into the handles.
Tighten your abdominal muscles and lift your knees up, so that you have a straight line from your head to your feet.
Keeping your legs straight, use your core muscles to pull your feet in towards your shoulders, lifting your hips up and moving your body into the jackknife position.
Control the movement as you lower your legs back to start position to repeat the exercise.
