Rest

"Can you stand up or will you just fall down?" Hole, Celebrity Skin

Are you resting enough when you exercise? This question touches a couple of bases:

• When you're weight training you should rest your body between 30-60 seconds between sets. This gives your muscles a moment to recover some energy and you a chance to catch your breath. Don't keel over, now!
• Don't work the same muscle groups two days in a row. Try to work your upper and lower body on alternating days. This will give your muscles optimum time to rest and recover and--gasp!--build.

If you continually work the same muscles over and over without any rest your muscles won't have a chance to recover. And you may not see the type of gains you want if you don't give your body time to do that. Visualize this: When you weight train you are ripping to shreds tiny microscopic muscle fibers. When you rest your body repairs those tears. As you increase the amount of weight that you train with your body figures that you need more fibers to help lift the weight. And that, my friends, is how you build muscle. Bottom line, treat yourself to a break.

For more information on the importance of rest while strength training check out this article.