Internal rotation of the hip is one of the most important aspects of a fast breaststroker.  At the Race Club, we like to measure the distance between the breaststroker's bum and the ground in what is referred to as the 'W' sit.  If you are able to get your bum 1" or less to the ground you  have the tools to be a fast breaststroker.  This is a unique attribute to a breaststrokers because most freestyle, backstroke and butterfliers have poor internal hip rotation.  We recommend a yoga block between your bum and the ground for these 'mortal' swimmers.  Once we measure the distance we have the swimmer go through a 10-10-10 stretch where each set of 10 is from a slightly different position.  After performing this static stretch you should see considerable improvement!  The key is to take the time and be consistent with this stretch.