Injuries and fatigue are, unfortunately, part of staying in shape, although of course, injury and fatigue are also part of being deconditioned and out of shape. The difference is the type of injury, the reason for the fatigue, and the way you handle both.

Exercising a lot is great, but exercising too much is dangerous. For one thing, your body needs rest as much as it needs activity. In other words, everything in moderation. Even professional athletes balance their intense workout programs with lots of rest because they have exerted themselves so much.

This is not to say you have to spend entire days sleeping or being inactive. It simply means that training — intense exercise with a goal — cannot be done seven days a week.

For example, you can take a walk every day, but you can't take an interval walk every day. You can swim every day, but some of those swims should be fun, not timed laps. If you do yoga every day, some of your poses should be restorative.

If you feel very tired, listen to your body and don't push yourself through a workout. Instead, give yourself a day of rest and understand that you will work out on the following day. Don't be afraid that you will stop exercising forever. The reality is that ignoring signs of overuse and overtraining tend to lead to stopping exercise, but appropriate rest will help you stay in shape and keep you motivated.

It's okay to exercise if you have a little cold, but anything more than that and you're overheating and overtaxing your body enough to make it difficult for your body to fight the infection or bug that is invading your system.

Cold symptoms include no fever or a very low one (99 to 100 degrees Fahrenheit), no body ache or a slight one, mild fatigue, and congested nose and sneezing. A cold comes on slowly, and having a headache with a cold is rare.

Flu symptoms are a high fever that can last three to four days, headache, body aches, and exhaustion (which can last up to a few weeks). The flu comes on suddenly, and congestion and sneezing are rare. You should never exercise when you have the flu, and, in fact, you should wait a few days and ramp up your routine slowly even after you're all better.