Lie face up, with your back flat on an exercise mat and knees bent at 90 degrees with your lower leg parallel to the floor. Extend your arms out to the sides, level with your shoulders in a T-position. This is your start position. Maintaining a 90 degree angle, move your knees to the left towards the floor. Do this slowly and with control thoroughout. Be sure to keep your core braced and not let your lower back arch as you lower your knees to the floor. Pause at the bottom of the movement, with your knees hovering an inch off the floor. Reverse the movement and perform the same movement on the opposite side. Perform this alternating movement for the required number of reps (or time).