Jennifer Lopez has been a fitness icon for the last three decades, and from the looks of her new behind-the-scene training video for Hustlers, she's not slowing down anytime soon. The actress/musician/mogul stars in the new crime thriller as a veteran dancer in a strip club, who devises a plan to scam her Wall Street clients with her co-workers by getting 'em drunk and racking up the charges. To nail the part, Lopez had to nail the physicality of a veteran stripper, which turned out to be no small feat, even for one of …