Celebrity Couples: Who's Healthy, Who's Not?

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Justin Timberlake and Jessica Biel

The Grammy-winning singer and the 7th Heaven actress have been photographed running together near their apartment in New York City. Both are serious about strength-training, as is evident by their toned physiques.

Timberlake shaped up with a grueling bootcamp while filming Alpha Dog in 2006, and Biel gets her famously toned arms by doing push-ups. “Everybody I train ends up doing push-ups at some point because they are so beneficial. They help you get incredible arms!” says Biel's trainer, Jason Walsh.

Tip to steal: Work out with your partner. It’s a great motivator and increases endorphins.

Next: Will Smith and Jada Pinkett