Negative training, also called eccentric training, focuses on the lowering phase of a weightlifting repetition rather than the lifting phase, explains Donald Chu, Ph.D., P.T., former president of the National Strength and Conditioning Association. "You're actually stronger when doing negatives," says Dr. Chu, "because you can lower more weight than you can lift."

What makes that added power possible? It is believed that more fast-twitch muscle fibers are recruited during eccentric contractions than during concentric contractions (which occur during the lifting phase). Not only do the additional fast-twitch fibers allow you to carry the extra load, but they also tend to respond well to resistance training—more so than slow-twitch fibers—therefore quickly becoming stronger and capable of handling increased weight demands. And the more weight you lift, the more strength you can build.

The downside, says Dr. Chu, is that you will also experience greater muscle soreness with negative training. Due to the fact that fewer muscle fibers overall are recruited in eccentric contractions, the fibers that are involved do more work and take more strain. But don't worry, the resulting stiffness subsides after three or four days and the level of soreness decreases dramatically after the initial exercise bout.

While it may seem a little macho, negative training has particular benefits for women. A recent study published in the journal Medicine & Science in Sports & Exercise found negative training strengthened bones (adjacent to the working muscles) more than standard weightlifting did, which means it can help women—who have a higher risk of osteoporosis—preserve and build bone.

To incorporate negatives into your routine, do your scheduled circuit of weights but minimize the lifting portion. Have a partner help you lift the weight, then lower it on your own. Or, for a double whammy, raise the weight in three counts and lower it in five, suggests Allen Hedrick, strength and conditioning coach the U.S. Air Force Academy. The muscle you gain will be worth the muscle pain.