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I've recently changed to an ashtanga practice as I thought I needed more cardio in my lifestyle. I've noticed that over a very short amount of time that I've really bulked up and I've got really big muscles on my arms which is understandable as we do so many push ups, but also on my thighs? I know this is a more physical practice but should this really be happeneing? I thought yoga was supposed to make you lean not bulk you up...is this just me or am I doing something wrong.

Really...You doing any poses that you wouldn't normally do.....Are you holding poses longer?
I'm only new to the yoga thing, but I do notice how some styles/teachers will make you hold longer and you can certainly feel the muscles burning/working more.

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Oh Dear......You really think i can get myself into that pose.........and then back out of it?