According to the Centers for Disease Control, approximately 90 percent of American adults are so sedentary they could almost be reclassified as statues (1). It should therefore come as no surprise that obesity has increased by almost 70 percent in the past 10 years (12% to 20%). Nearly 60 percent of all adults in this country are overweight, and the percentage of obese children has doubled since the 1980's. In addition to higher risk for heart disease and various types of cancer, obesity raises the risk of diabetes 10 times for men and 20 times for women (2).
Unfortunately, being overweight is merely the tip of the iceberg when it comes to body composition concerns. Sedentary adults typically add 10 pounds of bodyweight every decade during the midlife years. However, this unfavorable weight change results from a 5-pound loss of muscle and a 15-pound gain in fat. In other words, what appears to be a 10-pound weight problem is actually a 20-pound body composition problem (3).
In addition to adversely affecting personal appearance and physical performance, the reduction in muscle tissue is largely responsible for metabolic slow-down. The 5-pound per decade muscle loss is closely associated with a 5-percent per decade decrease in resting metabolic rate (4).
Even people who don't increase their food intake experience creeping obesity, because calories previously used to maintain more muscle tissue are now placed in fat storage areas of the body.
Most Americans know that they are adding fat, but few realize that they are losing muscle. What's more, they don't understand that muscle loss is a major factor in fat gain. If they did, they wouldn't place such a strong emphasis on dieting. With one out of every two adults presently following a low-calorie diet plan, we need a major teaching effort from health and fitness professionals to remedy this situation.
Although dieting can reduce fat, it cannot replace muscle to solve the primary body composition problem. In fact, low-calorie diets actually result in muscle loss, which accounts for approximately 25 percent of the total weight lost (5).
Fortunately, more overweight adults are complementing their diet plan with aerobic activity (usually walking) that burns additional calories and enhances cardiovascular fitness. While this combined program of diet and endurance exercise attenuates muscle loss, it does not add muscle or increase resting metabolic rate.
The missing component, of course, is strength training which does replace muscle tissue and recharge resting metabolism. Studies show that 25 minutes of standard strength training, two or three days a week, can increase previously inactive adults' muscle mass by about three pounds in two to three months of training (6,7,8,9). What's more, research reveals that three pounds of new muscle tissue increases resting metabolism by 6 to 8 percent, which represents an additional 100 to 120 calories per day (8,9).
Health Benefits of Strength Training
Strength training is the best means for attaining and maintaining a desirable body composition, as well as for developing a high level of musculoskeletal fitness. However, there are many other health-related reasons for performing regular resistance exercise. Consider the following medical benefits associated with sensible strength training.