Skinfold measurement is one of the most widely used tools in anthropometry for assessing body composition and monitoring a patient’s or athlete’s progress. For nutrition professionals, knowing how to measure and interpret these data correctly makes it possible to assess changes in subcutaneous fat, provide more accurate follow-up and avoid errors caused by relying solely on body weight or an estimated body fat percentage.
What is anthropometry and why is it essential in nutritional assessment?
Anthropometry is the discipline that studies the in vivo quantification of body components, their quantitative relationships and changes associated with various biological factors. In clinical settings, it is an essential tool for diagnosing nutritional status, identifying sarcopenia, classifying obesity, assessing cardiometabolic risk and monitoring malnutrition. In sports nutrition, its applications focus on monitoring the body’s adaptations to training and diet, managing weight categories in combat sports and optimising the relationship between fat-free mass and adipose tissue mass to enhance physical performance.
On the INDYA blog, we have a post discussing anthropometry and its importance.
Advantages over other body composition methods
Unlike complex laboratory technologies, anthropometry stands out for its accessibility, portability and low cost. Its greatest strength is its ability to detect subcutaneous adiposity. By measuring directly in millimetres, practitioners can track subtle changes in a patient’s fat without altering the data through mathematical conversion formulas that often obscure the reality of the tissue.
Limitations and margin of error
Despite its considerable usefulness in the field, anthropometry has inherent methodological and physical limitations that practitioners must understand to avoid compromising diagnostic quality:
- High dependence on the assessor (technical error of measurement). The human factor is a critical variable in this method. This potential variability can be reduced through training and standardisation under strict protocols such as ISAK, the leading international authority on anthropometry.
- Variable compressibility of adipose tissue. Subcutaneous adipose tissue is dynamic and deformable. Skin elasticity and the ease with which tissue compresses naturally vary with the person’s age, sex, skin turgor and hydration status.
- Dependence on the quality and calibration of the equipment.
- Difficulty applying the method at population extremes. For example, in patients with severe obesity, tissue thickness may exceed the maximum opening of the skinfold caliper or make it difficult to separate the double layer of skin and fat cleanly from the muscle.
What are skinfolds and what information do they provide?
The physiological basis of skinfold measurement
Skinfold measurement assesses the thickness of a double layer of skin and subcutaneous adipose tissue at specific anatomical sites. It involves applying constant pressure using mechanical calipers designed for this purpose.
Relationship with subcutaneous and total body fat
The central hypothesis of this technique is that subcutaneous fat has a close, proportional relationship with total body fat. Assessing multiple body sites together provides a representative, valid estimate of an individual’s overall adiposity. Recent studies comparing the technique with high-resolution ultrasound confirm that skinfold measurements provide reasonably accurate data.
Usefulness in patient follow-up
The sum of skinfolds acts as a direct indicator of changes in body composition. Working with absolute values in millimetres eliminates biases from prediction equations. In practice, a reduction in the sum of skinfolds mathematically confirms a loss of subcutaneous fat, providing patients and practitioners with real, objective data on the impact of nutritional intervention and exercise.
Main skinfold measurement sites
Triceps, biceps, subscapular and suprailiac
These four sites are the traditional skinfolds used in classic protocols, such as the Durnin–Womersley formula. They provide a quick, general estimate of adiposity. However, they are less adequate for assessing athletic populations because they do not give equal consideration to fat deposits in the lower limbs or deeper abdominal region.
Skinfolds in 6-, 7- and 8-site protocols
The different protocols are structured as follows to suit different needs:
- 6-skinfold protocol (Σ6): Includes the triceps, subscapular, supraspinale, abdominal, front thigh and medial calf skinfolds. It is established as the most balanced model in sports and clinical practice because it combines trunk (central) and limb (peripheral) skinfolds equally.
- 7-skinfold protocol (Σ7): Adds the mid-axillary or iliac crest skinfold.
- 8-skinfold protocol (Σ8): Includes the triceps, subscapular, biceps, supraspinale, iliac crest, abdominal, thigh and calf skinfolds. It provides detailed anatomical mapping, ideal for elite athletes.
Choosing a protocol for the context
While the sum of 4 skinfolds is useful for rapid screening in public health or general paediatric populations, the sum of 6 skinfolds (Σ6) is the recommended standard for monitoring competitive athletes and patients in nutrition practice because it offers an excellent balance between accuracy and time. Eight-skinfold protocols are reserved for highly precise scientific research or extreme aesthetic disciplines such as bodybuilding, where regional adiposity distribution needs to be characterised to the millimetre.
How to measure skinfolds correctly
To measure skinfolds correctly, we will follow the ISAK protocol. The steps are:
- Locating and marking: Identify the anatomical reference points using bony landmarks. Mark the exact site with a skin-marking pencil.
- Grasping the fold: Using the thumb and index finger of the left hand, pinch and cleanly lift a double layer of skin and subcutaneous tissue, ensuring that the underlying muscle remains relaxed and outside the grasp.
- Applying the caliper: Position the caliper jaws 1 cm below the assessor’s fingers, perpendicular (90°) to the skin surface.
- Taking the reading: Maintain pressure with the fingers of the left hand throughout the measurement and read the caliper exactly 2 seconds after releasing its jaws.
Using a skinfold caliper
It is essential to use a calibrated, constant-pressure skinfold caliper that applies a standard pressure of 10 g/mm², such as a Harpenden model. The instrument should have a resolution of between 0.2 and 1 mm. Regularly check that the needle reads zero when closed, and check calibration annually using gauge blocks to avoid biased readings caused by wear in the internal springs.
Controlling technical error of measurement
To ensure reproducible data, the anthropometrist should take at least two measurements at each site in an alternating, head-to-toe sequence, giving the tissue time to recover and avoiding the squeezing effect. If the two readings differ by more than 5%, take a third measurement and use the median as the final value. Each practitioner should also periodically calculate their technical error of measurement (TEM) to keep it within optimal limits.
Determining fat mass through anthropometry
Commonly used equations (Durnin–Womersley, Withers, Carter, Faulkner, Yuhasz…)
These mathematical equations estimate body fat percentage from body density calculated using sums of skinfolds. However, each was developed for a population with very specific characteristics. For example, the Yuhasz and Faulkner formulas were designed for athletes or active people, whereas Durnin–Womersley focuses on the general population. Applying an inappropriate equation produces drastic variations in the final result and unrealistic body fat estimates for the patient.
Estimating body fat percentage and adipose tissue mass
Fat mass or body fat percentage is often confused with adipose tissue mass. These are entirely different concepts that belong to different levels of human body analysis:
- Fat mass (chemical/molecular level): Refers strictly to pure lipids (triglycerides) that can be extracted chemically. It is assessed using classic two-component formulas (Siri, Brozek), equipment such as densitometry (DEXA), or the equations mentioned above.
- Adipose tissue mass (anatomical level): Refers to the entire adipose tissue. This tissue is not pure fat alone: adipose tissue consists of 80% lipids (fat), but also contains water, proteins, blood vessels, nerves and connective tissue. The most widely used formula for determining this value is the Kerr formula.
Adipose tissue mass will always be higher than fat mass in the same person. If ISAK software reports 20% adipose tissue mass using Kerr, the athlete does not have 20% pure fat; their chemical fat mass is probably 14–16%. Anatomical tissue and pure chemical fat cannot be mixed or compared as though they were the same thing.
Interpreting results
In performance-focused consultations, interpretation should prioritise the absolute sum in millimetres over estimated body fat percentage. If a body fat percentage must be reported, always use the same equation and measurement protocol at every appointment so that comparisons over time remain methodologically valid.
Other relevant anthropometric measurements
Body circumferences
Circumferences of the arm, chest, waist, hip, thigh and calf assess muscular development and changes in the regional distribution of body volume. Correcting certain circumferences by subtracting the thickness of the adjacent skinfold can provide very precise estimates of a particular muscle area.
Bone breadths
Bone breadths, including small measurements such as wrist bi-styloid breadth or humeral and femoral bicondylar breadths, determine skeletal robustness and proportionality. They are essential for separating total bone mass in multi-compartment models such as Kerr’s.
Derived indices (BMI, somatotype)
Body mass index (BMI) is a useful screening tool in the general population, but is less accurate in physically active people and athletes, where its correlation with actual adiposity is low or even negative because of the weight contributed by muscle tissue. Somatotype describes a person’s physique and body shape in three dimensions: endomorphy (high adiposity), mesomorphy (musculoskeletal robustness) and ectomorphy (low adiposity).
The ISAK protocol and measurement standardisation
Certification levels
The International Society for the Advancement of Kinanthropometry (ISAK) has an accreditation scheme structured into four levels:
- Level 1 (restricted profile): Training in basic measurements, small breadths and skinfolds.
- Level 2 (full profile): Covers all measurements, including the large bone breadths needed for five-component models.
- Level 3 (instructor): Qualifies practitioners to train anthropometrists at lower levels.
- Level 4 (criterion anthropometrist): The highest level of methodological and scientific recognition.
The importance of reproducibility
ISAK’s methodological standardisation ensures that a skinfold is measured using exactly the same anatomical and technical criteria anywhere in the world. This reduces subjective variability and allows practitioners and researchers to build and share global databases with full confidence that their records are equivalent.
Quality control in practice
Quality control in nutrition practice requires periodic calculation of the percentage technical error of measurement (%TEM). ISAK suggests that a well-trained assessor should maintain an intra-assessor TEM below 5% for skinfolds. Meeting this methodological standard ensures that recorded changes in the patient reflect real tissue changes rather than inaccuracies introduced by the assessor.
Applying anthropometry in nutrition practice
The first consultation establishes the patient’s or athlete’s baseline, identifying their fat distribution pattern and level of musculoskeletal development. This supports personalised nutrition and training goals.
Monitoring changes in body composition
Unlike other methods affected by external factors, sequential skinfold anthropometry stands out for its consistency over time. It allows practitioners to assess accurately whether weight loss truly reflects a reduction in subcutaneous adipose tissue or whether muscle mass is being compromised.
Combining results with other indicators
Anthropometric body composition results should never be assessed in isolation. They should be cross-referenced and analysed alongside dietary records, clinical blood biomarkers and the patient’s physical or sporting performance, such as improvements in speed, power or running economy, to gain a complete understanding of the athlete’s health and progress.
Common errors in anthropometric measurement
Poor technique or insufficient training
A deviation of just a few millimetres from the previously marked anatomical site, or incorrect caliper alignment relative to the skin’s tension line, significantly alters the reading. Insufficient training can push technical error of measurement (TEM) above 10%, making the data invalid.
Incorrect use of equations
A recurring error is applying predictive equations to populations whose ethnic characteristics differ from those of the original sample in which the formula was validated. For example, using equations designed for Caucasian populations in Asian individuals often underestimates actual adiposity.
Interpreting data in isolation
Focusing obsessively on a body fat percentage estimated by mathematical equations while neglecting health, functional performance and absolute values in millimetres is a serious conceptual error. The estimated percentage is only an indirect prediction; the direct sum in millimetres is the actual measurement.
Comparison with other body composition methods
Anthropometry vs bioelectrical impedance
Bioelectrical impedance analysis (BIA) is convenient and quick, but its mathematical algorithm is highly sensitive to the patient’s hydration status, previous food intake, ambient temperature and menstrual cycle phase. Skinfold anthropometry, by contrast, remains physically stable in the face of these transient physiological variables, providing much more consistent adiposity data over time.
We explain all the differences in this post.
Anthropometry vs DEXA
Dual-energy X-ray absorptiometry (DEXA) is considered an excellent reference method for assessing bone density and segmental lean mass. However, its high cost and lack of portability limit routine use. Acute changes in muscle water after intense exercise can also overestimate DEXA-measured lean mass by more than 1 kg, a bias that does not affect the sum of skinfolds in rested athletes in the same way.
When to choose each method
BIA and DEXA are excellent options for research laboratories or clinics where rigorous control of the patient’s hydration status can be guaranteed. For routine longitudinal monitoring of athletes in the field or everyday nutrition consultations, however, standardised anthropometry, especially the sum of 6 skinfolds, stands out as the method of choice because of its excellent cost-to-accuracy ratio and stability in the face of acute fluid changes.
How to improve accuracy and usefulness in practice
Standardising the protocol
Accuracy in practice improves dramatically when the international ISAK manual is followed strictly. Always marking anatomical reference points with an anthropometric tape and skin-marking pencil is a mandatory, non-negotiable step before applying the caliper.
Measurement frequency
Measuring too frequently has little practical value because real changes in body tissues, such as loss of adipose tissue or muscle hypertrophy, take time to become established. Full anthropometric assessments are recommended at intervals of 4 to 8 weeks, always ensuring that the patient or athlete attends in a rested state.
Combining measurements with clinical and performance data
In general, a progressive reduction in skinfolds should be related directly to improvements in sports performance, greater energy efficiency and prevention of cardiometabolic conditions. This provides more objective information about the athlete’s or patient’s progress, helping to improve motivation and adherence to the nutrition plan.
Conclusion
Skinfolds and other anthropometric measurements provide particularly useful information when collected using a standardised protocol and interpreted as part of the patient’s overall progress. Their value in practice lies in comparing measurements, identifying changes in body composition and relating them to diet, training and performance, rather than focusing on an isolated body fat percentage. With nutrition software such as INDYA, you can bring these data together with the patient’s other information and use them to provide more comprehensive, personalised follow-up.
Frequently asked questions about skinfolds and anthropometry
How accurate are skinfold measurements?
In the hands of properly certified anthropometrists, the technique offers excellent accuracy with a low technical error of measurement, usually between 3% and 5%. Its results show a fairly strong correlation with advanced techniques such as DEXA.
How often should they be measured?
Anthropometric follow-up is recommended every 4 to 8 weeks to allow structural and histological changes in adipose and muscle tissues to become established. More frequent measurement is not advisable because of normal fluctuations and the technique’s own margin of error.
Which protocol is best?
The sum of 6 skinfolds is established as the most representative, robust and balanced protocol for monitoring total subcutaneous adiposity in both athletes and clinical populations.
Can results be compared between practitioners?
Yes. Direct comparisons are entirely possible provided all practitioners involved hold current international certification, such as ISAK, and rigorously apply the same reference manual in a standardised way. Each anthropometrist may nevertheless retain a small margin of error.
References
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