I was browsing some time trial videos on YouTube and came across a video on saddle shuffling, and I've been noticing that I do the same saddle shuffle a lot when riding hard.  Did not really know it was a problem until I saw a [video][1] about it.  Is this common among riders?  My seat is correctly positioned too and it's perfectly level. I wonder how common this is...

http://youtu.be/2sYUfzHzYaU

*To anyone who can't see the video:* The problem is that a rider will, over time, shuffle forward on the saddle as they ride, every so often pushing themselves back so they're squarely on the saddle. 

**Edit:** About me:  I'm 5'6 about 145lb and ride a Specialized [Allez Apex][2]. I use clipless pedals and have received a [BG Bike Fit][3]. The bike size is a 52.  I would consider myself an aggresive rider.  


**Update:** So I thought I would update you with some tweaks I've done so far. I went to my LBS and purchased a shorter stem so I'm not leaning forward as much. I also measured my seat and myself [(sit bones)][4] and it showed that my seat was too narrow, though, I have been measured before and have always been told the seat was good (my other two bikes were the same). I was suggested to try the [Romin][6] or [Avatar][5] saddles. The look of the Romin seems like it will keep me from moving forward as much. I plan on testing the seats out in a trainer and around town. Thanks for all the suggestions.


  [1]: http://youtu.be/2sYUfzHzYaU
  [2]: http://www.specialized.com/us/en/bc/SBCProduct.jsp?spid=62277&scid=1101&scname=Road
  [3]: http://bicycles.stackexchange.com/questions/3549/bike-fitting-experiences
  [4]: http://www.specialized.com/specs/spec.jsp?speccode=bodygeometrysaddles&tablewidth=400&cellwidth=350
  [5]: http://www.specialized.com/us/en/bc/SBCEqProduct.jsp?spid=64272
  [6]: http://www.specialized.com/us/en/bc/SBCEqProduct.jsp?spid=64276