Reliability of Measurement Of Body Fat Composition

a.So are you fat or thin? what does it mean to your health?

The physical structure and the fitness of two people of the same height, body weight, and age may be completely different because they have a different body fat composition. This report examines the body composition by the study of relative measurements of body mass index (BMI), waist-hip ratio (WHR) and body fat percentage.

body fat men and women

 In physical fitness, body composition refers to the relative amount of body’s fat to the fat-free mass. Fat-free mass includes all the body fluids, muscles, bones and other tissues. Body fat consists of essential and non-essential fats located within fat cells and adipose tissue, below the skin and surrounding organs. Normal BMI and body fat percentage is necessary for a healthy lifestyle and to be physically fit for the activities especially which require high agility and endurance. According to the American College of Sports Medicine (2001), the normal or healthy body fat ranges are 8% to 22% in men and 20% to 35% in women.

The assessment or measurement of body composition is considered the major component of health-related fitness as it is always associated with increased heart diseases and other diseases (Powers and Dodd, 2003), which may lead to fatal accidents during physical or sporting activities. However, a certain level of body fat is necessary for the hormonal and thermal regulations, protection of internal organs, and also acts as an energy source during high endurance exercises/work.

How your body fat can be measured?

The available body composition measurement methods vary from simple field-based methods as anthropometry and bioimpedance analysis to more complex laboratory-based methods like DXA, hydrostatic weighing, air plethysmography, whole body counting for potassium, MRI, CT etc (Alison and Baskin, 2009). All methods have certain limitations and some degree of error in measurement.

Body Mass Index (BMI)

BMI is not always a highly reliable and accurate index of body composition as it uses only body weight as a whole and the height of the subject, regardless of the major component contributing to the body weight. Cronk and Roche 1982; Rolland-Cachera et al., (1982 as cited in Forbes, 1987), found that the average BMI is about the same for both sexes during the adolescent and young adult years despite the obvious difference in body fat content. However, BMI is a suitable method for measuring groups of individuals especially in field-based tests and also provides average accuracy provided maximum accuracy in measuring height and weight of the individuals.

Waist Hip Ratio (WHR)

WHR is commonly used to analyze the general fat distribution in the body. Alison et al., 2009, indicates the more central storage of fat with high WHR whereas more storage of fat in the femoral-glutei area with low WHR. The accuracy and validity of WHR are high with the measurement at the proper anatomical site. The reproducibility of waist circumference measurement was high, J. Wang et al., (2003, as cited in Alison et al., 2009) performed in triplicate over four sites for men and women (N=93).

Skinfold (SKF)

Skinfold measurements to calculate percentage body fat is the reliable non-invasive method of measuring body composition as it relies on the fact that over 50% of body fat lies just beneath the skin. However, at least two three measurements are required to get the most accurate percentage of body fat (Powers et al., 2003).

We use anthropometrical measurement method to assess the subjects’ body composition by measuring girth circumference and skin folds at different sites and thereby calculating the BMI, WHR, and percentage body fat (%BF).




Two subjects (both male students) who were physically fit, active and healthy volunteered to participate in the study. The experimental subjects 1 and 2 were 25 and 26 years of age and weighed 95.4 kg and 71 kg respectively. We informed both the subjects about the study procedures, protocol, safety measures, purpose, duration and benefits of the body composition measurement.


We measured total body weight and the standing height of both the subjects. After that we did girth measurements at various sites of the body namely; right upper arm, right forearm, buttocks, abdomen, right thigh and right calf in the first week of the study. Similarly, in the second week, we measured skinfold of both the subjects at various sites namely; biceps, triceps, subscapular, supraspinal, abdomen, thigh and calf. We calculated BMI, WHR and Percentage Body Fat from the obtained measurements.


All the measurements were taken with subjects standing erect in an anatomical position and on right side of the body. Each measurement was taken at least twice to improve the accuracy and reliability of the data obtained. If any data differed more than 0.5 cm then the measurement was repeated for that particular site. The measuring tape was used lightly so that to avoid the compression of the tissues by the tape pressure.

The landmarks for measurements were determined with great accuracy possible according to the standard literature. The skinfold was taken by using the flat pads of the index finger and thumb. The subject was told to contract and stretch muscles to avoid any involvement of muscle layer in a grasped skin-fold. The skin-fold caliper was then applied 1 cm from the fingers and placed to the depth of approximately mid fingernail. Measurements were taken two seconds after the full pressure of caliper was applied.

Equipment and calculations

Equipments Calculations
   Jadever Weight machine (JPS 2030)    Weight
   SECA stadiometer    Height
   KDS measuring tape of 2m in length    Girth measurements
   Skin-fold caliper of Slim Guide Creative          Health Products (Plymouth) SKF measurements

Equations to calculate BMI and WHR were;

BMI=Body Weight (Kg)/ (Height)2 in m2 and

WHR= Waist circumference (m)/ Hip circumference (m)

By using girth measurements, equation to calculate  %BF;

%BF= Constant A+B-C-10.2, where constants A, B and C are estimated from the standard constant conversion table for measuring %BF.

Similarly, by using SKF measurement,

%BF= (Sum of Six skin-folds) x 0.1051+2.588


Overall, both the subjects were overweight with BMI value more than 25 kg/m2. Subject 1 had just touched the class I obesity line with BMI 30.69 kg/m2 (Table 1). Along with the obesity mark, the waist/hip ratio of subject 1 is also increased in comparison to subject 2. This indicates the storage of excessive fat in the central part of your body (Allison et al., 2009).  However, we found a significant difference in the measurement of percentage body fat between the one we calculated from girth measurements to the result calculated from SKF measurements (Table 3), in the case of both subjects.

Table1: Height and weight of the subjects along with girth measurements at different sites of the body.


Subject No.


Girth Measurements





Right UA Right FA Abdomen Buttocks Right Thigh Right Calf    (kg)   (m)
1 38.5 30.0  93.5 111.5 62.4 40.0 95.4 176.3
2 33.5 29.7  83.7 95.4 56.6 39.3    71.0 161.8

  Table2: Two skin-fold measurements at each of the 7 sites of the body of both subjects. 

Skin-fold  Measurements

Subject No. Measurement No. Skin-fold Measurements
Triceps Subscapular Supraspinale Abdomen Thigh Calf Biceps
1  1 14.5 14.0 7.0 21.1 14.5 10.5 5.3
2 14.3 14.2 7.3 21.3 14.7 10.5 5.1
2 1 11.0 14.0 7.5 15.0 13.5 10.4 6.5
2 11.0 14.0 7.0 15.0 13.0 10.0 6.5

Table3: Final results calculated from the measurements recorded in table 1 and 2 (BMI, WHR, and %BF)

Subject No. BMI WWHR G%BF (Girth Measurement) %BF (Skinfold measurement)
(Kg/m2) % %
1  30.69 0.92 28.80 11.16
2  27.10 0.87 16.76 10.09


We found different assumptions of body composition from different methods of measurements we had used. So, the major finding of this study was that the determination of body composition by calculating BMI, girth measurement, and skin-fold measurement methods are not the most reliable methods. All the methods used have certain limitations. However, there were similar differences in the results of all the measurements between the two subjects (Table 3). This suggested average reliability and validity of the methods if performed more accuracy and repetitions.

body fat percentage

Body Mass Index

The BMI of both the subjects 1 & 2 were higher (30.69 & 27.10) which come under obesity and overweight class according to the classification given by U.S. Dept. of Health and Human Services 2000a, (as cited in Heyward and Wagner, 2004). But according to %BF level from skinfold measurement, both subjects have a mild increase in %BF than standard recommended level. BMI does not take into account Fat mass (FM) and Fat-free mass (FFM) separately of the total body weight. (Heyward et al., 2004). This clearly showed that both the subjects had high fat free mass rather than high body fat.

Percentage body fat

Similarly, %BF calculated by using girth measurements were significantly higher than the same from skin-fold measurements. We assumed that this difference may be due to the involvement of both FM and FFM in the girth measurements as in BMI. The accurate landmark marking for taking girth and skin-fold measurements require a high level of expertise and practice. Even a small difference in measurements can lead to significant difference in %BF calculated.(Biaggi, Vollman, Nies, Breener, Flakal, Levenhagen, Sun, Karabulut and Chen, 1996, p=901). We performed this measurement for the first time which might have affected the calculation or result.

The positioning of the subject and condition of muscle mass (for example; abdominal girth measurement during full inspiration definitely give higher abdominal circumference measurement than in expiration state) might have resulted in higher %BF by girth measurements. Since we included only upper body sites in girth measurements, %BF calculated is higher than that from skin-fold which also include lower body measurements. This is also supported by the higher WHR ratio (0.92) for subject 1, which signifies the more distribution of fat towards the central part of the body (Heymsfield, Lohman, Wang and Going, 2005).

Skinfold measurement

The skinfold method is more reliable and accurate method of calculating body fat. It only includes the skin and subcutaneous fat level while holding the skin-fold and is more reproducible. However, the technician’s skill, type of SKF caliper, subject factors and the prediction equation used to estimate body fatness highly affects the validity and reliability of SKF measurements, Lohman, Pollock, Slaughter, Brandon and Boileau (1984, as cited in Heyward and Stolarczyk, 1996). The density of FM and FFM also affect body fatness. But SKF measurement assumes constant densities which affect significantly in %BF calculate.

The standard New Zealand population data shows the significant increase in the percentile groups of obese and overweight people. When we compared our subjects’ sum of six SKF measurements with that of normative data of New Zealand population based on the sum of six SKF measurements, both come under the average percentile group. Subject 1 in 65 percentile groups and subject 2 in 55 percentile groups. So, compared to New Zealand population data, %BF calculation to our subjects was considerable according to their age group and level of physical activity.


The validity and reliability of body composition measurement depend upon the type of method used, the expertise of the technician, subject factors, materials and protocol used for the calculation of %BF. The measurements we used generally provide higher values of body fatness as they didn’t purely separate the accountability of FM and FFM in total body weight. Also, there were many limitations and error factors. However, BMI, skinfold and girth measurements are considerable ways of field measurement and large-scale studies. Therefore, these are also simple and cost effective methods to determine body composition if performed with good expertise and accuracy.



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