Thirty minutes of aerobic exercise, such as walking or cycling, three to five days per week has long been known to help prevent cardiovascular disease.

Latest development: A recent study published in Circulation, the journal of the American Heart Association, concluded that strength training is equally important for maintaining healthy cholesterol levels and blood pressure—and even more critical for preventing diabetes and boosting the body's metabolism, which helps burn calories and prevent weight gain.

Why is this type of exercise so important? Researchers have found that regular strength training is the only way to prevent the five-to seven-pound loss in muscle mass that all adults—except trained athletes—experience each decade beginning in their mid-20s.

That's why the American College of Sports Medicine (ACSM) now recommends that, in addition to regular aerobic workouts, all adults perform two or three strength-training sessions per week. Each workout should last 20 to 40 minutes and consist of eight or more exercises that work all the major muscle groups of the body.

There's just one problem: If you walk into a health club or local YMCA, you're likely to encounter a bewildering array of strength-training classes that claim to "firm and tone your body," "build lean muscle mass" or some combination of the above. Which type of class is right for you?

Any class you're considering should be supervised by a trainer who has been certified by a national fitness organization, such as the ACSM or the American Council on Exercise. When properly supervised, strength training is one of the safest forms of exercise there is even among elderly and frail adults.

Caution: Your muscles require 48 to 72 hours to recover from each strength training workout Adults age 50 or older should strength train every three days.

What you need to know about strength-training classes…

Body Sculpting

What it does: Tones muscles, while moderately increasing strength and muscle tissue.

These classes include a variety of strength-building exercises, using elastic resistance bands, dumbbells, medicine balls (handheld, weighted exercise balls) and calisthenics. A typical body-sculpting class consists of eight to 15 different exercises that work all the body's major muscle groups. Each exercise should involve 20 repetitions or less, and take no more than two minutes.

While body-sculpting classes don't produce as much gain in strength and muscle mass as other types of strength training exercises, they will increase lean muscle tissue somewhat, and are highly effective at increasing functional muscle strength (used for lifting and carrying).


What it does: Strengthens the "core" muscles of the low back, front abdominal muscles and oblique muscles that run from the back of the abdomen to the front.

Pilates classes use slow-moving stretches and resistance exercises to increase flexibility and strength. These moves are performed using Pilates equipment (pulleys and weights set on a frame) or without equipment on a floor mat.

*If you prefer at-home exercise, Tufts University and the Centers for Disease Control and Prevention (CDC) have created a strength-training program called "Growing Stronger." It can be downloaded for free from the CDC Web site, www.cdc.gounccdbpb/dnpa/physical/growing...stronger/. Click on "Resources. Or you can purchase it at

Caution: If you have back pain, check with a doctor before taking Pilates classes to be sure you have no structural abnormalities that might be exacerbated.

Note: Core-training classes offer benefits that are similar to those of Pilates and typically consist of a variety of resistance exercises using calisthenics, medicine balls, lightweight dumbbells, resistance bands and inflated stability balls (which you sit on while exercising)-all designed to activate and strengthen the low-back and abdominal muscles.

Weight Training

What it does: Builds strength and muscle mass.

When it comes to increasing strength and muscle mass, no other form of strength training comes close to matching standard weight training. Weight training typically involves about 10 different resistance exercises covering all the major muscle groups. They can be performed with weight machines (such as those made by Nautilus or Cybex) or free weights (barbells and dumbbells). In each exercise, a weight is lifted eight to 12 times in a slow, controlled fashion.

Research has found that weight training increases the glucose uptake of the body's muscles by nearly 25% (reducing the risk for diabetes), and lowers blood pressure by an average of 4 mmHg systolic (top number) and 2 mmHg diastolic (bottom number over periods of two to four months. By stimulating the skeletal system, it also can help maintain bone density.

Circuit Training

What it does: Combines the maximum strength- and muscle-building benefits of weight training with an aerobic workout that benefits the cardiovascular system.

In a circuit-training class, exercisers perform about 10 weight-training exercises for one minute each. Between these strength exercises, a minute or two of aerobic activity (such as riding a stationary bicycle or walking/jogging on a treadmill) is performed.

These classes are excellent time-savers, since they offer the benefits of weight training and an aerobic workout in a single session of 30 to 45 minutes. Due to the aerobic component, circuit training also burns about 50% more calories per workout session than standard strength training classes.

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