I've got them too - depressions across both thighs at the same height (about 1/2 ways between knee and groin), this is about the same location as where a pair of cycle pants would end (don't actually wear them). They formed about 6 weeks ago (I think, don't really make a habit of inspecting my thighs - definitely noticed them about this time). Routine - workout every week day morning before work, about an hour, alternating cardio and weight training, moved to low impact cardio (treadmill over 1/2 hour 40 mins up to incline 8 and down again) about 4 months ago as achilles started playing up), do yoga 2-3 times weekly. Only other factors I can think of is move to duplex in May with 4 flights of stairs (great for quads) and internal stairscase + skiiing for first time this year (shortly before these formed) - am going to see osteopath this week to see if he has any ideas... Will let you know if he has any theories or suggestions.
I have the same problem! I don't work out or lift weights. (I'm going to be screwed when my metabolism slows down.) But, I'm twenty years old and male, and a few months ago I noticed these indentations. Its like someone layed a heavy bar across the middle of my thighs. You can't see them unless you're looking for them, but when you run your hand acrossed,, you can definitely feel them. Idk what in the world it is. It doesn't hurt, but I don't think its normal. I'm glad I'm not the only one, though.