Body Composition Definitions Medical literature: The term overweight refers to an overfat condition, despite the absence of accompanying body fat measures. Obesity refers to individuals at the extreme of the overfat continuum. The overweight condition simply refers to a body weight that exceeds some average for stature, and perhaps age, usually by some standard deviation unit or percentage.
Reference Man and Reference Woman The reference man is taller and heavier, his skeleton weighs more, and he has a larger muscle mass and lower total fat content than the reference woman. Reference man: Fat 15% of total body mass Reference woman: Fat 27% of total body mass
Essential and Storage Fat Essential fat consists of the fat stored in the marrow of bones, heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues of the central nervous system. Normal physiologic functioning requires this fat. Storage fat depot consists of fat accumulation in adipose tissue. Reference man: approximately 12% storage fat Reference woman: approximately 15% storage fat
Fat-Free Body Mass and Lean Body Mass Lean body mass (LBM) contains a small percentage of essential fat stores equivalent to approximately 3% of body mass. Fat-free body mass (FFM) represents the body devoid of all extractable fat. In normally hydrated, healthy adults, FFM and LBM differ only in the “essential” lipid-rich stores in bone marrow, brain, spinal cord, and internal organs.
Skinfold Measurements The rationale for using skinfolds to estimate body fat comes from the relationships among three factors. Fat in the adipose tissue deposits directly beneath the skin (subcutaneous fat) Internal fat Whole-body density The most common anatomic locations for skinfold measurement include the triceps, subscapular, suprailiac, abdominal, and upper thigh sites.
Skinfold Measurements (cont.) Requires grasping a fold of skin and subcutaneous fat firmly with the thumb and forefingers and pulling it away from the underlying muscle tissue following the natural contour of the skinfold The pincer jaws of calipers used for precise measurement exert a constant tension of 10 gmm -2 at the point of contact with the caliper. The caliper dial indicates skinfold thickness in millimeters, which is recorded within 2 seconds after applying the full force of the caliper.
Bioelectrical Impedance Analysis (BIA) A painless, localized electric current is introduced, and the impedance (resistance) to current flow is determined between the source and detector electrodes. Conversion of the impedance value to body density— adding body mass and stature, gender, age, and sometimes race, level of fatness, and several girths to the equation—computes percent body fat from the Siri equation or another similar density conversion equation.
Near-Infrared Interactance Assesses body composition in humans using principles of light absorption and reflection Safe, portable, and lightweight equipment requires minimal training to use and necessitates little physical contact with the subject during measurement. Available data do not support NIR as a robust, valid method to assess human body composition.
Dual-Energy X-Ray Absorptiometry Quantifies fat and nonbone regional lean body mass, including the mineral content of the body’s deeper bony structures and muscle mass Clinical tool to assess spinal osteoporosis and related bone disorders Computer software reconstructs the attenuated x-ray beams to produce an image of the underlying tissues and quantify bone mineral content, total fat mass, and FFM.
Sport-Specific Observations The Elite Athlete Olympic and Elite Athletes Field Event Athletes Female Endurance Athletes Male Endurance Athletes Triathletes Swimmers versus Runners American Football Players Professional Golfers