Lean body mass positively affects metabolism, muscular strength and immune system function. Alternatively, excess fat increases your risk for diabetes, hypertension and other weight-related diseases. Your amount of lean body mass depends on many factors, including sex, age and physical-activity level. Although you can understand factors of lean body mass, only body-fat assessment estimates your body composition.
Body Composition
Body composition categorizes body weight as either fat or fat-free mass, also known as lean mass. Lean mass includes muscles, bones, organs and connective tissue. Although you can easily measure your body weight, body-composition assessment requires testing beyond standard body weight assessment. While body-fat percentage defines your amount of total weight comprised of fat, subtracting your body-fat percentage from 100 provides your percentage of lean body mass.
Sex Factors
On average, men acquire more lean body mass than women. A typical man, between 18 and 35 years old, maintains 13 percent body fat, or 87 percent lean mass, while a typical woman, aged 18 to 35, possesses a body-fat percentage of 28 percent, or 72 percent lean mass, according to the book "Advanced Fitness Assessment and Exercise Prescription." Because men possess greater levels of muscle-building hormones, they naturally amass more muscle than females.
Age Factors
Lean mass declines with age. According "Advanced Fitness Assessment and Exercise Prescription" 18- to 35-year-old men average 2 to 11 percent greater lean mass than men older than 55. Furthermore, 18- to 35-year-old women average 2 to 8 percent more lean mass than women older than 55. Because men typically maintain less body fat and greater muscle mass than women, men have more lean mass to lose as age progresses. Regular exercise may slow or reverse effects of sarcopenia, or age-related loss of muscle mass. Additionally, lean mass declines with age as bone density decreases.
Physical Activity Level
Regular weight-bearing activity enhances lean mass regardless of age, sex or previous activity level. For example, weight-bearing activity, such as resistance training or walking, builds muscle mass and bone density. While active individuals require greater exercise intensity for adaptation, untrained individuals require lower intensity. For instance, a senior adult who has not exercised in two years may increase lean mass by walking 20 minutes, three days per week. Conversely, a 25-year-old man who plays soccer may require four hours of weekly resistance training for enhanced lean mass. Therefore, you should consult a doctor or fitness professional for an individualized lean-mass building exercise program.
References
- "ACE Personal Trainer Manual"; American Council on Exercise; 2003
- "Advanced Fitness Assessment and Exercise Prescription"; Vivian H. Heyward; 2006
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