Q: I hope this isn't too basic a question for you, but how do muscles get bigger and stronger? - K. B., Evanston, IL

A: Let me first say that the more you know about what is going on with your body when you train, the better athlete you will become, so don't ever feel embarrassed about asking questions. Muscles get bigger and stronger through something called overload. For the muscle to get bigger, you must overload it. To do this, you stress the muscle in both intensity and duration beyond the demands of previous activity. This is followed by a rest period during which the muscle rebuilds with greater strength and endurance. The muscle's cells are programmed to rebuild more strongly so they can handle greater stress the next time.

If you want to make gains in strength, you need to increase the resistance (weight) your muscle is bearing. For gains in muscular endurance, you need to lower the resistance and increase the number of repetitions you perform. As your muscles adapt to the increased stress, you must overload them even more for further gains. In 300 B.C., Milo of Croton demonstrated this principle of progressive resistance training by carrying a calf every day until it became a full- grown bull.

Source: fitlinxx.com