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Body Composition: Measurement
Techniques to Increase Accuracy
Q:
A:
When making assessments related to body
composition, what are simple measures that
can provide accurate information?
Body composition is one of the health-related
physical fitness components identified in ACSM's
Guidelines for Exercise Testing and Prescription, 11th
edition (ACSM's GETP11), along with cardiorespiratory endurance, muscular strength, muscular endurance, and flexibility (1).
Body composition is described as “the relative amounts of muscle,
fat, bone, and other vital parts of the body” (1). Anthropometric
methods involve looking at measurements and proportions. These
include height and weight, which when combined mathematically
provide body mass index and circumference (1). Although these numeric values are descriptive and potentially helpful in assessing
Box 1. Relationship between obesity and health risk
Obesity is described as a “multifactorial disease with
complex pathogenesis related to biological, psychosocial,
socioeconomic and environmental factors and heterogeneity
in the pathways and mechanisms by which it leads to
adverse health outcomes” (2). With an estimated 39% to
49% of the global population being overweight or obese (2),
concerns regarding health risk make body composition
determination of value. BMI in the overweight and obese
classifications is generally related to increased risk of
various health conditions (3), although this is not true for
individuals with large muscle mass for whom BMI may be
above 25 kg·m−2 (overweight) or above 30 kg·m−2 (obese
classification) because weight in relationship to height is
high. Waist circumference and waist-to-hip ratio may better
reflect visceral adiposity, which is a risk factor for
cardiovascular disease (2), as visceral fat around the organs
is more metabolically active and is thus linked with metabolic
dysregulation (4). Obesity is associated with increased risk
of type 2 diabetes (overweight increases risk of developing
type 2 diabetes threefold and obesity by a factor of seven
compared with normal weight), heart disease and ischemic
stroke (as well as risk factors for these disease: dyslipidemia
and hypertension), many cancers (including associations
with increased risk for esophageal, colon, pancreatic, breast,
endometrial, and renal cancers in addition to concerns for
several other cancers), mortality in-hospital, and major
complications of surgery (4).
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health risk (see Box 1 for background on associations between obesity
and health), body mass index and circumference do not reflect the
actual composition of the body — the amount of fat and muscle.
The only method to directly determine total body fat is by
cadaver dissection; thus, indirect methods are necessary (5).
Indirect techniques such as hydrostatic weighing and air displacement plethysmography provide needed insight on body
volume, which in turn is used to calculate body density and
subsequently percent body fat (5). For more on these methods,
see Box 2. Skinfold measures are considered anthropometric
Box 2. Determination of body density: hydrostatic
weighing and air displacement plethysmography
Body density determination reflects the ratio of body mass
to body volume (1). Based on cadaver-based studies,
equations have been developed to allow for conversion of
body density to percent body fat (6). Body mass (i.e., body
weight) is simple and can be accurately measured. Body
volume is more challenging; methods include hydrostatic
weighing and air displacement plethysmography (trade
name BOD POD) (see Figure 1).
Hydrostatic weighing is considered the “gold standard” for
determining body volume and is based on Archimedes
principle, which explains that a body under water is buoyed
up by a force equal to the weight of the fluid displaced (7).
Very simply, this method looks at the individual's body
weight on land and when completely submerged in water —
this latter aspect is where the term “underwater
weighing” originates. The heavier the person is in the
water, the greater the density; the lighter, the lower the
density (e.g., someone who easily floats). The person sits
on chair/frame that is suspended from a scale to measure
weight when submerged; factors related to water
temperature, residual volume in the lungs, and gas in the
gastrointestinal tract are involved in the final calculation of
body volume and body density (8) (see Figure 2).
Another method to determine body volume is air
displacement plethysmography. In this case, specialized
equipment (e.g., BOD POD) measures displacement of air.
The BOD POD has two chambers — one where the
individual sits and one that is a reference chamber; a
flexible, airtight diaphragm between the two chambers
allows for determination of the volume taken up by the
individual (6). As with hydrostatic weighing, body volume
measurement then allows for body density determination
which is then used to estimate percent body fat.
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Figure 1. Body volume measurement using air displacement plethysmography (trade name BOD POD). Used with permission
of Mayo Foundation for Medical Education and Research, all rights reserved.
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measures and have been described as “doubly indirect” given
that the skinfold thickness is used in prediction equations along
with an individual's age to estimate body density, which in turn
allows for calculation of body fat percentage (i.e., the percent of
the total body weight that is fat) (1,5).
Given the specialized equipment and costs associated with
hydrostatic weighing and air displacement plethysmography,
the focus of this article will be on anthropometric measures that
are relatively simple and inexpensive, providing valuable insights
when done carefully and consistently according to standardized
procedures.
Figure 2. Hydrostatic weighing is used to measure body
density in order to obtain measures of body composition.
Photo courtesy of the Department of Exercise Science and
Sport Management at Kennesaw State University. Used
with permission.
BODY MASS INDEX (BMI)
BMI is a mathematical calculation that reflects an individual’s
body weight relative to height; the calculation is as follows: body
weight in kilograms (kg) divided by height in meters squared
(m2). The unit of measure is kilograms per square meter (or this
may be written as kg·m−2). Body weight should be determined
on a calibrated scale (balance beam or electronic) with no shoes
and minimal clothing (i.e., shorts and T-shirt) (7). A stadiometer
is a device with a vertical ruler and sliding horizontal platform
that is lowered to the top of the person’s head to measure height.
Height should be determined with shoes off, heels together,
standing with head, buttocks, and heels in contact with the vertical ruler; the individual should breathe in and hold breath
while looking forward while the horizontal platform is lowered
to touch the top of the head (7).
With accurate height and weight measures, BMI can be calculated. A sample calculation is shown in Box 3. Classification
by BMI includes the following: underweight is less than 18.5 kg·m−2,
normal is 18.5–24.9 kg·m−2, overweight is 25–29.5 kg·m−2,
and obesity is 30 kg·m−2 and above (1). Although often used
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Box 3. BMI calculation
For an individual with a weight of 154 lbs and a height of
70 inches:
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First convert weight from pounds to kilograms (kg); there
are 2.2 lbs in each kilogram:
154/2.2 = 70 kg
Then convert height from inches to meters (m); there are
0.0254 meters in each inch:
70 inches 0.0254 = 1.78 m
To complete the calculation, take the weight in kilograms
and divide by the height squared
BMI = 70/(1.782)
BMI = 70/(3.17)
BMI = 22.1 kg·m−2
Another option for determining BMI is to use an online
calculator. This calculator allows you to enter either
standard or metric units and then the BMI is provided in
kg·m−2: https://www.nhlbi.nih.gov/health/educational/
lose_wt/BMI/bmicalc.htm.
on a population level to determine “obesity,” a shortcoming of
BMI is the inability to look at composition or to differentiate fat
from muscle (1). For example, a muscular strength-trained individual with a low percent body fat can have a BMI above
30 kg·m−2. An obesity classification for this individual would be
inappropriate as the “excess” weight relative to height is muscle
rather than fat. Other assessments, including girth (circumference)
or skinfold measures, would be more helpful in this situation.
CIRCUMFERENCE
Measurement of waist circumference, or determination of the
ratio of waist and hip circumference, can be used to reflect the
pattern of body fat distribution (1). Body fat that dominates on
the trunk is referred to as android obesity; body fat in the hip
and thigh area is referred to as gynoid obesity (1). Android obesity
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is associated with increased risk of hypertension, type 2 diabetes,
dyslipidemia, cardiovascular disease, and metabolic syndrome,
among other health concerns (1). Circumference measures are
simple and can be used to reflect general distribution of body fat.
Ideally, the measurements should be made with a tape measure
with spring-loaded handle (see Figure 3 for an example), which
allows for better consistency between measures as the tension on
the tape can be standardized (1). Without the spring mechanism, differing measures could result simply by altering the
amount of tension on the tape (i.e., holding it tightly or more
loosely). Two measures should be taken, allowing for time between a single measure or rotating through sites, with an average of two measures within 5 mm being used.
The waist circumference focuses on central obesity. The location of “waist” is not universally defined (9); for more insights into
the various definitions, see the prior ACSM's Health & Fitness Journal® article “A Simple yet Complicated Tool: Measuring Waist
Circumference to Determine Cardiometabolic Risk.” ACSM's
GETP11 defines waist as “at the level of the iliac crest” (1), as
shown in Figure 3. High risk according to this measurement site
begins at 90 cm (35.5 inches) for women and 100 cm (39.5 inches)
for men (1). Note that the population on which these risk criteria
are based is limited (Caucasian), and thus values reflecting risk
may be different for other racial and ethnic groups (1).
Waist-to-hip ratio involves a slightly different measure for “waist”
along with hip circumference (1,7). The ratio requires a calculation:
waist circumference divided by hip circumference (1). The individual should be standing with arms at sides and feet together. The abdomen should be relaxed, in a neutral position. For this ratio, waist
is measured as the narrowest part of the torso above the umbilicus
and below the xiphoid process. The hip is measured with the tape
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Box 4. Description of skinfold sites (adapted from
ACSM [1]) (https://youtu.be/cEsuxgX2Udg).
Figure 4. Components of a fold (skin and subcutaneous
fat) and location of caliper (blue mark). Photo courtesy of
Barbara Bushman.
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Abdominal: vertical fold located 2 cm to the right of the
umbilicus
Suprailiac: diagonal fold located above the anterior superior
iliac spine (i.e., anterior axillary line immediately above the
iliac crest)
Triceps: vertical fold located midway between the acromion
process of the scapula and the olecranon process of the ulna
in the posterior midline with arm held freely at the side
Thigh: vertical fold located midway between the inguinal
crease and the proximal border of the patella in the
anterior midline
Subscapular: diagonal fold located 1–2 cm below the inferior
angle of the scapula
Chest (for males): diagonal fold located midway between the
anterior axillary line and the nipple in men
at the maximal circumference of the buttocks. For both the waist
and the hip girth measures, ensure that the tape measurement is
in a horizontal orientation around the entire circumference of the
waist and hip, respectively. For individuals younger than 60 years
of age, health risk is high when the ratio is >0.95 for men and
>0.86 for women (1). For individuals 60 to 69 years of age, high
risk is >1.03 for men and >0.90 for women (1).
SKINFOLD MEASURES
Skinfold measures correlate with more technical methods of
body fat determination (i.e., hydrodensitometry and air displacement plethysmography). The basic premise is that the amount of
subcutaneous fat is proportional to the total body fat (1). Although generally about one-third of body fat is subcutaneous,
many factors can affect this, including differences in intra- and
intermuscular fat and fat deposits in internal organs along with
variations for males and females, age, and race (1).
Figure 3. Waist measurement with spring-loaded handle.
Skinfold assessment can predict percent body fat within
±3.5% fat (1). That level of accuracy assumes proper techniques
were used with correct determination of skinfold location and
properly calibrated skinfold calipers (1). A “fold” should include
two layers of skin and the underlying subcutaneous fat (see
Figure 4). Locations of selected sites are defined in Box 4. Pictures of the sites are found in Figures 5 to 9. Note that the marks
on the skin are oriented to allow for consistent placement of the
caliper (on the “cross bar”), while the other line should be the
“top” of the fold (see Figure 10 A and B). Taking care in measuring and marking these locations will improve accuracy and is a
key aspect of skinfold measures.
Standardized testing is key for accuracy and includes the following (1):
Figure 5. Abdominal and suprailiac skinfold locations.
Photo courtesy of Barbara Bushman.
Photo courtesy of Barbara Bushman.
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• Measures should be done on the right side of the client’s
body
• The pinch should be maintained throughout the measurement
• Caliper placement should be directly on the skin (not over
clothing)
• Caliper should be 1 cm away from the fingers pinching the
fold to avoid compressing the fold being measured (see
Figure 10 for correct and incorrect distancing)
• Caliper should be placed halfway between the top of the
fold and the base (see blue bar in Figure 4)
• Allow the caliper to settle for 2 seconds before taking the
reading, open caliper jaws to remove from skin after measurement is noted
• Repeat measurements should be taken by rotating through
the sites to allow for each area to return to normal between
measures
• Measures should be within 2 mm
Figure 7. Thigh skinfold location. Photo courtesy of
Barbara Bushman.
At least two measures per site are required, within 2 mm of
one another. If the initial two measures are not within 2 mm, take
an additional measurement, using the mean of whichever two
measures were within 2 mm of one another for the calculations.
Figure 6. Triceps skinfold location. Photo courtesy of
Barbara Bushman.
Skinfold equations have been developed for males and females with various combinations of skinfold measures, along
with age, allowing for calculation of body density. Box 5 shows
two options that each require three skinfold site measurements
for men and women. The calculated body density is then used
to estimate percent body fat. One commonly used equation is
as follows (1):
Figure 8. Subscapular skinfold location. Photo courtesy of
Barbara Bushman.
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Figure 9. Chest skinfold location (male). Photo courtesy of
Barbara Bushman.
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although normative values suggest a range of 12% to 23%
for males and 17% to 26% for females as “good” (1). Other
factors, including age, sex, race, and athletic level, are additional considerations regarding what best reflects a healthy percentage of body fat (1).
SUMMARY
Anthropometric measures allow for indirect determination of
aspects related to body composition. Weight in relation to height
(i.e., BMI) provides general insight, although BMI is unable to
discriminate between difference in weight due to excess fat compared with muscle. Circumference measures (hip girth and
waist-to-hip ratio) are helpful in gauging distribution of body
fat and, thus, may be of better insight than BMI regarding health.
An indirect assessment of body composition is possible with the
skinfold technique, which requires care in measurements of subcutaneous fat to calculate an estimate of percent body fat. The determination of body composition may thus be made with simple
tools and is a valuable addition within fitness assessments.
Box 6. Example skinfold test results with calculation
of percent body fat
33-year-old male
Percent body fat = [(4.95/body density) − 4.50] 100.
Thus, the steps are to record the skinfolds required, complete
the matching calculation for body density, and then mathematically convert body density to percent body fat. An example is
found in Box 6. A healthy percent body fat has not been defined,
Box 5. Equations to determine body density from
skinfold measures (1)
Male
Three-site formula requiring sum of chest, abdominal,
and thigh measures (SS) and age in years
Body density = 1.10938 − (0.0008267 SS) +
(0.0000016 SS2) − (0.0002574 age)
Three-site formula requiring sum of chest, triceps, and
subscapular measures and age in years
Body density = 1.1125025 − (0.0013125 SS) +
(0.0000055 SS2) − (0.000244 age)
Female
Three-site formula requiring sum of triceps, suprailiac, and
thigh measures and age in years
Body density = 1.0994921 − (0.0009929 SS) +
(0.0000023 SS2) − (0.0001392 age)
Three-site formula requiring sum of triceps, suprailiac,
and abdominal measures and age in years
Body density = 1.089733 − (0.0009245 SS) +
(0.0000025 SS2) − (0.0000979 age)
Volume 26 | Number 2
Site
Measurement 1 (mm)
Measurement 2 (mm)
Mean (mm)
Chest
12
14
13
Abdomen
14
14
14
Thigh
16
18
17
For the calculation, the sum of the three skinfolds is
44 mm (13 + 14 + 17 = 44).
The next step is to enter the sum of the skinfolds and age
in years into the equation from Box 5 reflecting these three
sites (these values are shown in bold; other values are the
constants in the regression equation)
Body density = 1.10938 − (0.0008267 44) +
(0.0000016 442) − (0.0002574 33)
Body density = 1.10938 − (0.0008267 44) +
(0.0000016 1936) − (0.0002574 33)
Body density = 1.10938 − (0.0363748) +
(0.0030976) − (.0084942)
Body density = 1.0676086
The body density (do not round this number) then can be
entered into the equation to convert to percent body fat:
Percent body fat = [(4.95/body density) − 4.50] 100
Percent body fat = [(4.95/1.0676086) − 4.50] 100
Percent body fat = 13.7%
For a 33-year-old male, this is in the “excellent” fitness
classification category, per ACSM's GETP11 (1).
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Figure 10 A and B. Skinfold showing proper distance of 1 cm between pinch and caliper and incorrect technique. A, Proper.
B, Incorrect. See video for both improper and proper skinfold technique: https://youtu.be/RdQ0UUblQ8E. Photos and
video courtesy of Barbara Bushman.
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1. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and
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wt/risk.htm.
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a narrative review of the efficacy of common body composition methods in applied
sports practice. Nutrients. 2021;12:1075. Available from: https://www.mdpi.
com/2072-6643/13/4/1075.
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8. Brodie D, Moscrip V, Hutcheon R. Body composition measurement: a review of
hydrodensitometry, anthropometry, and impedance methods. Nutrition. 1998;
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9. Serviente C, Sforzo GA. A simple yet complicated tool: measuring waist circumference to
determine cardiometabolic risk. ACSMs Health Fit J. 2013;17(6):29–34. Available
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Simple_Yet_Complicated_Tool__Measuring_Waist.7.aspx.
Barbara A. Bushman, Ph.D., FACSM,
ACSM-CEP, ACSM-EP, ACSM-CPT, is a
professor at Missouri State University.
Dr. Bushman has authored papers related
to menopause, factors influencing exercise
participation, and deepwater run training;
she authored ACSM’s Action Plan for
Menopause (Human Kinetics, 2005),
edited both the first and second editions of ACSM’s Complete Guide to Fitness & Health (Human Kinetics,
2011 and 2017), and promotes health/fitness at www.
Facebook.com/FitnessID.
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