The guidelines and attitudes about exercise during pregnancy have changed considerably through the years. Previous guidelines allowed a woman to walk one mile a day, ideally broken up throughout the day. Then the 140 beats per minute (BPM) limit guideline was instituted. While our knowledge of this particular area of exercise physiology is still incomplete, we now know a lot more about the benefits and risks of exercising during pregnancy. As a result, much more specific guidelines have been established.