Did you know that there is no natural movement for you to do a leg extension? However if you want to do them there is no reason you can't do them on the same day, as a matter of fact the only thing there good for is the final burn at the end of your work out. The should not be the primary exercise in a leg routine. Squats, squats, and squats.

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The Fool say in his heart "There is no God"