Sounds like for the near future your heart rate monitor will be your guide. Nothing wrong with riding flats if you can get your heart rate where you and your doctor think it needs to be. Good luck and happy riding.
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831