Anthropometry – Assessment of Body Composition

Anthropometric measurements are non-invasive and easily obtained measurements with a wide range of utility in both paediatric and adult populations, including athletes. They can be used to diagnose risk factors, enhance performance and help patients to assess improvement after treatment.

To enhance long-term patient outcomes, an inter-professional team should work together to consistently obtain reproducible results that apply to clinical settings. Accurate serial measurements over time are the most important aspect of anthropometry for a reliable indicator of risk factors.

This will help identify at-risk individuals early, help promote a healthy lifestyle, and enhance performance in athletes. Choosing the appropriate assessment method depends on aim, resources, population, and required accuracy.

Key Words: BMI, Skinfolds, Ultrasound, Waist-to-Height-Ratio (WHtR), Waist Circumference

Assessment of body composition can provide valuable information about one’s general health, nutritional adequacy, bodily development, but also about (sports) performance. Anthropometric measurements are quantitative measurements of the body, for which non-invasive tools and methods exist. In the paediatric population, anthropometric values are used to determine development and health status of the child (12). In adults, such measurements can help to assess health and nutritional status, as well as potential risk factors for diseases, such as obesity (13). In athletes, assessing body composition plays a key role in monitoring performance and training routines, especially in weight class and aesthetic sports (1).

The main components of anthropometry are height, body weight (and thereby body mass index (BMI)), as well as body circumferences and measurements used to estimate one’s body composition.

Accurate, regular anthropometric assessments can help identify underlying medical, nutritional, or social problems in children (3, 5) and adults. Body composition is an important health and performance variable, which is why in adults, anthropometric measurements are recommended at each visit to the physician in order to determine nutritional status and the risk of future disease. Further, in athletes, improved body composition has been associated with increased strength and cardiorespiratory fitness (15, 32).

Single, one-time assessments are non-advisable since accurate serial measurements over time are the most important aspect of anthropometry for a reliable indicator of risk factors. Depending on population and interest, different (more or less accurate) measurement methods exist to assess body composition. Those most relevant for the general population as well as athletes are outlined here.

In order to assess characteristics of the human body accurately, it is essential to use validated and reliable methods, best lined out in a standardised protocol, such as suggested by ISAK (International Society for the Advancement of Kinathropometry; 34). Further, it is crucial that only well-trained individuals perform such measurements and that the subject’s physical and emotional well-being is not compromised at any time during the assessment. Therefore, the following aspects should be considered before any assessment, independent of method or equipment.

- To insure privacy, measurements should be taken in a separate, private room or in a screened off area
- The option to be accompanied by a friend or parent should always be offered, especially when examining children
- Personal space should always be respected, which is why most measurements should be taken from the side
- Wherever possible, the person measuring the subject should have enough space to move around the subject easily and manipulate the equipment without hindrance. Too little space can lead to inaccurate measurements
- Equipment and the measurer’s hands should be cleaned before and after any measurements are taken
- Cultural sensitivities and socio-cultural aspects of touching should be considered, including cultural believes in the matter of dress.

The most frequently used assessment methods including necessary equipment and field of use are described thereafter.

Height
A person’s height is assessed using a stadiometer, which is ideally attached to the wall and the floor should be level and hard (34). Height is measured using the stretch method and defined as the “perpendicular distance between the transverse planes of the most superior point on the skull when the head is positioned in the Frankfort plane and the inferior aspect of the feet” (34). Therefore, the subject has to stand with closed heels, buttocks and upper part of the back touching the scale and the head levelled in the Frankfort plane (lower edge of the eye socket in the same horizontal plane as the notch superior to the tragus of the ear). When aligned, the highest point on the skull is used as reference for a person’s height.

Body Weight
Body weight assesses a person’s body mass using calibrated (electronic) scales. Regular and certified calibration of all scales is critical, as well as its tare before every use. When weighing, the subject stands on the centre of the scale distributing the weight evenly on both feet without support.

Since body weight displays circadian variation it is important to record the time measurements are taken.

Body Mass Index (BMI)
The BMI is frequently used as a measure of adiposity. To calculate the BMI, body weight is set in relation to the subject’s height (kg/m2). It is used for weight classification in large populations (39).

The BMI, however, is solely a relative measure of weight and does not take into account a person‘s individual composition of body mass from fat and muscle tissue, body shape, or gender. The cut-offs (Table 1) also underestimate obesity risk in certain populations, such as elite athletes and body-builders.

Therefore, BMI is insufficient as the sole means of classifying a person as obese or malnourished. Yet, to determine risk of obesity, BMI measurement is suggested for all persons two years or older. For children, age- and gender-specific BMI percentiles/z-scores are recommended (e.g. 24).

Mass Index (MI)
An alternative measure of relative body weight that considers the individual’s sitting height (s) and thus, implicitly, the leg length, is referred to as the mass index (MI = 0.53 m/hs), with m being body weight and h= body height (1, 21). The BMI and MI are equal when the ratio of sitting height and body height s/h = 0.53 (1, 21). The WHO cut-offs for underweight, overweight, and obesity (21) can remain the same when replacing the BMI by the MI.

Circumferences
The most commonly measured girths are waist and hip circumference, which can be used to estimate body fatness. In order to assess circumferences accurately, a flexible, non-extensible tape, no wider than 7 mm, and ideally made out of steel should be used (34).

Waist Circumference
Waist circumference is measured at its narrowest point of the abdomen “between the lower costal border (10th rib) and the top of the iliac crest, perpendicular to the long axis of the trunk” (34). Subjects stand with their arms folded across the chest, measurement is taken at the end of a normal expiration (end tidal). If there is no obvious narrowing, it should be measured at the mid-point between the lower costal border and the iliac crest.

Subjects with a waist circumference of ≥ 88 cm and ≥ 102 cm for women and men, respectively, are classed as abdominally obese (4); in children, age- and gender specific values are available (24). Waist circumference is recommended to be performed regularly in clinical practice (26).
Hip Circumference

To assess hip circumference, the tape is passed in a horizontal plane across “the buttocks at the level of their greatest posterior protuberance, perpendicular to the long axis of the trunk” (34). Subjects stand with their arms folded across the chest and the gluteal muscles relaxed.

Waist-to-Hip-Ratio (WHR) and Waist-to-Height-Ratio (WHtR)
As an indicator of health or the risk of developing diseases, waist-to-hip- (WHR) or waist-to-height-ratio (WHtR) can being calculated. WHR is determined as waist circumference divided by hip circumference. WHtR refers to the relationship between waist circumference and height. In contrast to the widely used BMI, those ratios are supposed to display body fat distribution and thus allow greater significance with regard to health relevance of being overweight (28).

Both ratios are used as an indirect measure to determine abdominal obesity, which is defined as a WHR of > 0.90 for men and > 0.85 for women (38), and a WHtR of ≥ 0.5 (independent of gender, 14). Higher values indicate a greater risk of obesity-related cardiovascular diseases (CVD; 17).

An increase of 1 cm in waist circumference is associated with a 2 % increase in risk of future CVD and an increase of 0.01 in WHR is associated with a 5 % increase in CVD risk (8). Whereas WHR has been found to be an effective predictor of mortality in older people (25), WHtR is to be used with care when examining children below the age of five (17, 36).

Body Composition Analysis
In order to assess body composition as a whole or in certain parts, there are reference methods with high levels of accuracy, as well as field methods that differ in validity as they often represent indirect measurement of body composition. Among the reference methods, multi-component models, specifically the 4-component model using measurements of body density (hydrodensitometry), total body water (via deuterium dilution method), and bone mineral (via dual energy X-ray absorptiometry (DEXA)), is the leading reference method for body composition analysis (1). DEXA measurement has the ability to simultaneously measure bone, lean, and fat mass status, which is crucial in the assessment of athletes suffering from Relative Energy Deficiency in Sport (RED-S) – a condition that affects bone health as well. Yet, DEXA use for assessment of whole body composition still suffers a lack of general reference data even creating difficulties when comparing results from different systems (31). Still, the use of (multiple) lab-based techniques is costly and time-consuming and thus impracticable for large studies (1), therefore, for practitioners more relevant field methods are described thereafter.

Hydrodensitometry and Air Displacement Plethysmography
Hydrostatic weighing is the current gold standard technique for measuring a person’s body density. It measures the displaced volume of water in order to determine body density; body composition can be estimated thereafter. Air displacement plethysmography is a similar densitometric method based on the same principle – displacing volume of air, rather than water. This two-component model that assesses mass and volume and therefore an estimation of body density, provides an estimation of fat and fat-free mass (FFM). Both methods are highly reliable and valid (10) but require very expensive acquisitions and estimation errors can occur due to different hydration status and movement while being measured (especially for air displacement plethysmography).

Computed Tomography (CT) and Magnetic Resonance Imaging (MRI)
CT and MRI can quantify muscle mass and quality (9) as well as abdominal fat mass. Due to the different magnetic properties of water and fat-bound protons, MRI allows to assess lean and adipose tissue compartments. Thereby, cross-sectional areas of skeletal muscles at distinct anatomical landmarks can provide accurate surrogates of total skeletal muscle amount and therefore may be used to identify patients with low muscle mass (7). Aspects such as sarcopenia may not be sufficiently captured by conventional anthropometric measurements such as BMI or WHR, particularly in obese patients (7).

Abdominal adipose tissue is often assessed using MRI, including visceral adipose tissue mass (23). Exact pictures of subcutaneous adipose tissue however, are sometimes difficult to obtain, as image resolution can be too coarse if insensitive coils are used or (especially with obese patients) the field of view is not large enough to image the whole cross section (20). Thus, equations overcoming this are available (20).

Therefore, MRI or a combination of CT and MRI can obtain adipose tissue measurements from routine diagnostic protocol with high correlation to MRI whole-body examination adipose tissue volumes (19). For the validated protocol in adult population, a single CT and MRI slice at the L2-L3 vertebral level is used (30) and recently, gender-dependent reference normative values of MRI-derived visceral and subcutaneous adipose tissue in children have been published (19).

Bioelectrical Impedance Analysis (BIA) and Fat-Free Mass Index (FFMI)
One estimate of body composition, especially muscle mass and body fat percentage, is bioelectrical impedance analysis (BIA), where weak electric current flows through the body in order to measure the voltage to then calculate impedance of the body. It is based on the assumption that a more muscular person also has more body water, which leads to lower impedance, which can then be used to estimate total body water and thereafter, fat-free mass (FFM). Thus, a fat-free mass index (FFMI; FFM/height2) can be calculated giving an estimate of health risk.

BIA can be more accurate if upper and lower body parts are utilised. Generally, BIA is accurate for measuring large samples, but is of limited accuracy for tracking individual body composition over a period of time, and not suggested for precise measurements of individuals (10). BIA equations and cut-off values are population and device-specific, therefore, results should always be interpreted with caution. Still, BIA can provide valuable data in athletes as a compliment to other techniques such as skinfolds, circumferences or air displacement plethysmography.

Measurements of Subcutaneous Adipose Tissue Skinfolds
The measurement of skinfold thickness is a widely used and simple approach to indirectly estimate body fat. Skinfolds provide linear measurements of a double layer of skin and underlying subcutaneous adipose tissue (SAT) in a compressed state (16). The reliability of this technique depends strongly on the skills of the observer and standardisation of the technique with precise measurement sites is essential (1).

ISAK developed a standard protocol with instructions for accurate site marking and skinfold measurement at eight body sites located on the trunk, arms, and legs (34).

Researchers and practitioners should be cautious of using population-specific equations to estimate body fat at the individual level (1, 18). The validity of such equations relies on several assumptions: skinfolds need to be of constant compressibility; skin thickness is the same at all sites, fat fraction and patterning of SAT is constant; as is the ratio of external to internal adiposity (18). However, none of these assumptions hold true (6, 18). Instead, raw skinfold data can be used to assess adiposity and describe fat patterning. This includes recording individual skinfolds, the sum of skinfolds, the ratio of two skinfolds or groups of skinfolds, and computing average skinfold depth across a number of sites. These values can be used for comparisons of individuals with group data/population norms or for longitudinal assessment especially in athletes, where assumptions of constant density and proportions of the components of fat-free mass are highly questionable (18).

It must further be pointed out that skinfold measurements do not allow assessment of visceral adipose tissue, which is associated with greater health risks.

Ultrasound
A novel, non-invasive approach to directly measure uncompressed SAT using brightness-mode ultrasound imaging has been developed (22, 35) and applied to various populations including athletes (e.g., 21), overweight and obese adults (35), and children (e.g. 16). Using portable ultrasound devices, this method can be applied both in the field and in clinical settings.

This imaging technique captures skin, SAT, muscle fascia, and underlying muscle tissue at eight body sites representing the trunk, arms, and legs. It was standardised in cooperation with the IOC Medical Commission Research Group on Body Composition, Health, and Performance by site marking, imaging, and image evaluation (22). With this approach, SAT thickness can be measured with an accuracy not reached by any other methods and limited only by biological factors. Measurement reliability is the overall limiting factor of this approach (21). High reliability can be obtained when measurements are performed in accordance with the standardized protocol and observers are well trained, as demonstrated in children, adults and across a wide range of SAT thicknesses (16, 21, 22, 35).

Using this technique, studies have shown that ultrasound measurements revealed differences in fatness between individuals and at the group level that were undetected by commonly used anthropometric measures such as the BMI (e.g. 16, 35).

The use of SAT thickness sums for comparisons between athletes is recommended and preliminary normative data for SAT thickness sums of the eight standard sites are available (2). As with skinfolds, visceral adipose tissue is not assessed with this approach.

The methods described in this brief overview do not cover the multitude of measurement techniques available for body composition analysis and focuses only on the most commonly used approaches applicable in the field setting. Therefore, no claim is made to completeness. Table 2 gives an overview of the aforementioned methods including application purpose and resources needed.

Those methods are non-invasive but there are situations in which the measurements might give inaccurate results or are impossible. In such situations these measurements can give alarming or falsely reassuring data and should avoided. Otherwise, regular, reoccurring measurements are specifically advised in order to identify potential health risks early.

Conflict of Interest
The authors have no conflict of interest.