Side Split, Middle Split, Center Split or Straddle. Side Split has many names. Full Straddle, Middle Split, Center Split, American Split, Chinese Split and Russian Split. Possible the reason for so many names is because for many mastering a Side Split is a bench mark of flexibility. Besides looking good and being a neat party trick, the Middle Split is also applicable to many sports and disciplines. Martial Arts Kickers, Dancers, Gymnasts, Figure Skaters, Cheerleaders, Sumo Wrestlers, Dancers and many others can benefit from an ability to do a Center Split.
Standard methods of mastering this split involve torture, PNF, Isometrics, etc. Yes, torture, since having people stand on you and push you down or pull your legs apart, while you cry out in pain can't be called a picnic. Other methods listed involve various muscles contractions combined with relaxation periods. The later work faster, but still involve pain and risk of injury.
Kinesiological stretching techniques do it the smart way and not the hard way. The stretch reflex is not wrestled with, but rather is avoided. So pain and injury don't stop the progress. Each muscle is isolated and get's manipulated through muscle space created, using various muscles actions against each other. Having tested various methods against each other. This is the safest, most pleasant and faster method known today.