Place one foot through the handle of a resistance tube, grasping the shaft of the tube at a comfortable resistance point with the hand on the opposite side of the attached foot. Starting in quadruped position on hands and knees, hands directly below shoulders and knees directly below hips, extend the attached leg straight back and up and the opposite arm forward and up. Keeping the back in a neutral position, and keep the abs engaged. Return to starting position with both hand and knee touching the ground. Repeat for the required number of repetitions before switching arms and legs.