As a transport medium for oxygen, nutrients, waste products and other substances, blood literally is your body's lifeline. Cardiac output plays the key function of delivering blood to your body tissues.
Scientific studies dating as far back as the 1950s have observed a link between cardiac output and body composition--body fat and lean-mass content.
Cardiac Output
Howard University professor of medicine Otello Randall defines cardiac output as the amount of blood that the left ventricle of your heart pumps out through the rest of your body every minute. Expressed in liters per minute--or L/min--cardiac output is the product of your heart rate and stroke volume. Your heart rate simply reflects the number of times your heart beats per minute, while your stroke volume is the amount of blood each beat moves. Any increase in either heart rate or stroke volume also causes cardiac output to rise.
Normal Values
At rest, your cardiac output approximately equals the volume of blood in your body, which is 5 liters, or 10 pints. This is the amount of blood that circulates from your heart through your body, and back to your heart every minute. When you exercise, cardiac output increases in proportion to exercise intensity and your fitness level. According to Randall, well-trained athletes, such as bicyclists and swimmers, can generate a cardiac output as high as six times their resting cardiac output.
Lean Body Mass
A simple definition of lean body mass is "non-fat mass," or the combined mass of your body fluid, muscles, bones and organs. In a 2001 issue of the American Heart Association's journal "Circulation," Hawaii-based internal medicine specialist Tarquin Collis and colleagues stated that 20 to 40 percent of weight gain can come from added fat-free mass. Direct measurement methods for your body composition include: skin fold calipers; bioelectrical impedance; hydrostatic underwater weighing; and dual-energy X-ray absorptiometry. The Medical College of Wisconsin also offers a body mass index calculator with readouts of your lean body mass--or LBM--based on your total weight and height. Note, however, that such indirect calculations only give rough estimates of your LBM.
Body Types
Based on percent body fat data from the Northwestern Health Sciences University, your LBM should represent 82 to 85 percent of your total weight if you're an adult male, and 75 to 78 percent if you're a female. LBM percentages below the above-mentioned ranges would mean that your body contains too much fat. In contrast, a higher percent LBM would classify you as "lean." Male athletes, for instance, often have more than 90 percent of LBM, while the value for their female counterparts commonly exceeds 83 percent.
Age Effects
Based on Vanderbilt University's age-adjusted body-fat data, recommended LBM percentages follow a downward trend as your age increases. For instance, adults between the ages of 20 and 29 should normally have a percent LBM ranging from 76 to 84 percent for women and 83 to 93 percent for men. In contrast, beyond the age of 60, the recommended lean body mass drops to ranges of 67 to 78 percent for women and 75 to 83 percent for men.
Considerations
A strong relation exists between cardiac output and fat-free mass, says Collis. The organs, tendons, ligaments and bones comprising your LBM represent the bulk of your body's metabolism. Therefore, your cardiac output must increase in proportion to your LBM gains in order to provide enough oxygen to sustain the increased metabolic demands. Collis and colleagues further note that stroke volume follows the same trend, suggesting that the cardiac output elevation mainly comes through an increased stroke volume.
References
- "The A to Z of the Heart and Heart Disease"; Deborah Romaine and Otello Randall, M.D.; 2006
- "Circulation"; Relations of Stroke Volume and Cardiac Output to Body Composition; Tarquin Collis, M.D. et al.; February 2001
- Vanderbilt University: Body Fat Percentage
- New Mexico State University: Body Composition
- Northwestern Health Sciences University: Body Mass Index (BMI) Versus Body Fat
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