All About Weight Training Forget diamonds. Iron is actually a girl’s best friend — when you pump it. Strength training becomes especially important once you hit 40. It builds and maintains muscle mass, protects the health of your cardiovascular system. and prevents weight gain (which in turn lowers your risk of type 2 diabetes, a common precursor of heart disease). It keeps your blood pressure in check, boosts your mood, staves off depression, ramps up your energy, and improves your balance. If you’re not doing it now, you should. Here are answers to the most common questions.Won’t strength training make me look bigger?Maybe — at first. "Sometimes, you do get a little bit bigger, because you’re building muscle before you’ve burned off fat," says Nancy Cummings, a research manager at the National Training Center in Clermont, Florida. But once you burn off the fat (which weight training will help do), you’ll look tighter. Because muscle is denser and more compact than fat, your body becomes smaller. You may not drop pounds, but you will lose dress sizes. "Your stronger muscles will hold you in and cinch your core," she says. How often and for how long do I really need to do it? Twice a week for 20 minutes is enough for the average woman to add about three pounds of muscle within 10 weeks. "The stimulus for growth maxes out after two evenly spaced weekly workouts," says Wayne Westcott, PhD, author of Building Strength and Stamina. "If you do three weekly sessions, you’ll burn more calories, so you’ll lose more fat."One set? Three? The American College of Sports Medicine recommends doing one set of eight to 12 reps for each exercise, but you’ll build endurance and burn more calories if you do more sets. "Aim for one to three sets," Westcott says. "There’s no need to do more than that."Is it true that lifting weights very slowly is more effective than the usual pace? "When you lift slowly, you’re training your muscles to be slow," Cummings says. "You don’t want muscles to respond slowly, so why would you train them that way?" But lift too quickly, and you’ll be using momentum, not muscle. Lift at an even, natural rate.All About WeightsWhich is better: lighter weights and more repetitions, or heavier weights and fewer repetitions?Do both. "Using lighter weights with higher reps — 12 to 15 — when you’re starting out will condition your muscles," says exercise physiologist Tom Holland, creator of the DVD Tom Holland’s Total Body Workout. "Then after about four weeks, adding weight and dropping the reps to 10 to 12 will build more strength." If you alternate between these methods every four weeks, adding more weight progressively, it will keep your muscles constantly stimulated and continue to shape them.Which comes first, weights or cardio? If you routinely combine the two in one session, start with cardio; a study from Brigham Young University shows you’ll burn more calories that way (always a nice bonus). Plus cardio can feel tougher after a weight workout. But if you occasionally combine both in one session, don’t stress about which comes first. "Mixing it up prevents plateaus and boredom," Holland says.Are bands as effective as weights? Bands can actually work you harder. "Picture doing a biceps curl: When you pull on a band, it gets more difficult as you move through the range of motion because the band is getting stretched to its maximum," says Annette Lang, a New York City personal trainer. "With a hand weight, it gets easier as you lift because the weight will be balanced directly over your arm bone." Check the band’s resistance by stretching it to 50 to 75 percent more than its resting length. If it’s too easy to pull, switch to one made of thicker material (most bands come color-coded for light, medium, or heavy resistance). To buy bands, check the Institute of Human Performance. Also available on the site: The Essence of Band and Pulley Training series (DVD, $99.99), by Juan Carlos Santana, which shows more than 100 band exercises.Institute of Human Performance site I have weak ankles and knees. Should I skip strength training? Muscles brace your joints; strengthening them supports and stabilizes your knees and ankles and prevents injuries.