Well, we know how it got that way!
The 45-year-old singer was doing a tough arm workout with trainer Tracy Anderson, and even though J. Lo's body had all of our attention, Miz Anderson couldn't say the same.
She stopped mid-workout to crouch and read another page from Lena Dunham's new book Not That Kind Of Girl.
Miz Lopez's reaction was pretty priceless!
Ch-ch-check it out