For three decades we’’ve heard endlessly about the virtues of aerobic (increasing oxygen consumption) exercise. Medical authorities have praised running and jumping as the key to good health, and millions of Americans have taken to the treadmill(踏车) to reap the rewards. But the story is changing. Everyone from the American Heart Association to the surgeon general’’s office has recently embraced strength training as a complement to aerobics. And as weight lifting has gone mainstream, so has the once obscure practice known as "Super Slow" training. Enthusiasts claim that by pumping iron at a snail’’s pace-making each "rep"(repeat) last 14 seconds instead of the usual seven-you can safely place extraordinary demands on your muscles, and call forth an extraordinary response. Slow lifting may not be the only exercise you need, as some advocates believe, but the benefits are often dramatic. 　　Almost anyone can handle this routine. The only requirements are complete focus and a tolerance for deep muscular burn. Fox each exercise-leg press, bench press, shoulder press and so on-you set the machine to provide only moderate resistance. But as you draw out each rep, depriving yourself of impetus, the weight soon feels unbearable. Defying the impulse to stop, you keep going until you can’’t complete a rep. Then you sustain your vain effort for 10 more seconds while the weight sinks gradually toward its cradle. Intense Uncomfortable Totally. But once you embrace muscle failure as the goal of the workout, it can become almost pleasure. 　　The goal is not to burn calories while you’’re exercising but to make your body burn them all the time. Running a few miles many make you sweat, but it expends only 100 calories per mile, and it doesn’’t stimulate much bone or muscle development. Strength training doesn’’t burn many calories, either. But when you push a muscle to failure, you set off a pour of physiological changes. As the muscle recovers over several days, it will thicken-and the new muscle tissue will demand sustenance. By the time you add three pounds of muscle, your body requires an extra 9,000 calories a month just to break even. Hold your diet steady and, very quickly, you are vaporizing body fat. 　　One might have benefited from any strength-training program. But advocates insist the slow technique is safer and more effective than traditional methods. Many Americans have taken to treadmill for years by virtue of