Hi----
I personally am dead center between the large and medium sizes by the asterisk charts.....i was intending to go with the large......as it appeared to follow my thigh contour a bit better then the medium. However when i went thru the set-up----specifically setting the extension limits i found with the large braces i could still hyper extend no matter what i had the limits at and how snug the fit to the leg was......so i bought the mediums. my experience with these (and other simular equip) is if you do not git it right, and set-up right---it wont do its job when you need it.