The Journal of Experimental Biology just published a study that told women who have worn high heels for long periods of time to not switch to flats.  In the study, the high heel wearers complained of discomfort wearing flats after steadily wearing heals for two or more years.  Scientists determined that high heel wearers had muscle fibers 13% shorter than women who wore flats.  Scientists also said that not only are muscle fibers shortened, tendons become thickened and stiff. 

The study recommended wearing heels and flats on alternating days, and if you must wear heels, try stretching exercises at the end of the day.  This hits close to home because I always wear heels.  Even my flip flop sandals are elevated   here is a link if you would like to see a summary of the study: 

Do you consistently wear high heels?  Do you notice any pain when you wear flats?