ARE YOUR MUSCLES SPAGHETTI?

Think of your muscles like spaghetti strands: They're pliable when they're warm, but fragile when they're not. That's why it's so important to warm up your muscles for about 5 minutes before beginning any exercise. The simplest way is to do an easier version of the same activity you'll be doing (so walk if you're planning to jog, use light weights before heavy ones, etc.). Move your joints through the same motions they'll go through during the upcoming activity. This will raise your heart rate and increase the temperature of your muscles, making them less prone to injury.

Warming up and stretching helps you burn more calories and sleep better. When warming up, focus on your muscles, and take special notice of where you tense up. The shoulders and forehead are common tension points. You want stretching to release tension in your body, not shift it somewhere else. Notice this, and focus on the muscles you are working. And make sure to keep breathing freely and slowly. You might feel a little discomfort or muscle burn as you're loosening up, but not actual pain. If you ever feel pain during stretching, stop.

Reference: YOU: On a Diet. Roizen, M. F., Oz, M. C., New York: Simon & Schuster, 2006.