Lie face up, with your back flat on an exercise mat. Your legs should be fully extended in the air, at a 90 degree angle to your torso. Whilst your arms should be extended above you, parallel to your legs. This is your start position. Proceed to lower your right leg towards the floor. Simultaneously extend your left arm directly behind you and overhead towards the floor. Be sure to keep your core braced throughout and not let your lower back arch as you lower your leg and arm. Pause at the bottom of the movement, with both right leg and left arm hovering an inch off the floor. Reverse the movement and perform the same sequence on the opposite leg and arm. Perform this alternating movement for the required number of reps (or time).