Competitive swimming consists of four strokes and utilizes both upper and lower extremities in moving forward through the water. Shoulder and arm mechanics are similar in the freestyle, butterfly, and backstroke. Much of the forward propulsion created during the pull-through phase of these strokes is the result of lift forces produced by the traversing motion of the hand and forearm. Shoulder adduction and internal rotation are important in stabilizing the shoulder and allowing the body to be moved forward over the hand during swimming. The same is true of the rapid motion portion of the breaststroke pull-through. Similarly, the flutter, or dolphin, kicks used in freestyle, backstroke, and butterfly produce forward motion by creating forward lift, and the lower leg "paddles" against the water. Knee motion is from approximately 0 to 90 degrees. In breaststroke, water is "whipped" out from between the rapidly closing legs; flexion is up to 140 degrees. All these forces are meant to overcome drag, which is the force resisting forward motion. It is hoped that at some time in the near future the determinants of drag will be measurable and correctable, therefore leading to more efficient, and faster, swimmers.