If you've worked hard to get in shape, the last thing you want is for your fitness gains to disappear. But if you skip your workouts for just two weeks, that's exactly what might happen, at least on some level. While people who are in shape can generally regain their fit physique easier than those who are starting from scratch, it may sound somewhat surprising that your body can fall so quickly out of shape. The phrase "use it or lose it" applies when it comes to your muscle strength, cardiovascular fitness and more.