Myth: It takes at least two weeks to get 'out of shape.'

Truth: In most people, muscle tissue can start to break down within a week without regular exercise.

"If you stop training, you actually do get noticeable de-conditioning, or the beginnings of de-conditioning, with as little as seven days of complete rest," Shawn Arent, director of the Center for Health and Human Performance at Rutgers University, said. "It very much is an issue of use it or lose it."

[Photo via @sweatwithbec]

2 of 12