Skinfold measurements are a common, accessible method used to assess body composition, particularly in fitness and general health settings. This technique is one of the oldest field methods for estimating total body fat percentage, relying on the measurement of fat located just beneath the skin’s surface. Skinfolds provide a simple, non-invasive way to track physical changes. Despite the development of more advanced technologies, this method remains a relevant tool for individuals and professionals monitoring changes in physique over time.
Skin Folds as a Body Composition Tool
The underlying principle of skinfold testing is that a significant proportion of the body’s total fat stores are held directly beneath the skin, known as subcutaneous fat. By measuring the thickness of these subcutaneous fat folds at specific body sites, professionals can estimate the total amount of body fat. This approach relies on the assumption that the distribution of subcutaneous fat is consistent and proportional to total body fat across individuals. Measuring subcutaneous fat provides a useful proxy for overall body fat percentage. The method inherently does not measure visceral fat, which is stored deeper within the abdominal cavity around internal organs. The primary goal of using skinfold measurements is to track relative changes in fat mass and distribution over time, rather than obtaining a single, perfect number.
Standardized Measurement Techniques
The physical measurement of skinfolds requires specialized tools called calipers, such as Harpenden or Lange models, which are designed to exert a constant pressure on the fold of skin. The technique involves the tester firmly grasping a double layer of skin and the underlying adipose tissue between the thumb and index finger, carefully pulling it away from the muscle. The caliper jaws are then applied about one centimeter away from the fingers, at a right angle to the fold, and the reading is taken in millimeters (mm) a few seconds after the caliper pressure is released. To minimize error, a trained technician must follow a standardized protocol, often taking two or three measurements at each site and using the average value.
Common measurement sites are chosen because they represent a significant portion of the body’s subcutaneous fat distribution. These sites often include:
- The triceps
- The subscapular area beneath the shoulder blade
- The suprailiac region just above the hip bone
- The abdomen
Consistency is paramount; using the same caliper, technician, sites, and time of day for subsequent tests helps ensure the data accurately reflects changes in the individual’s body.
Converting Raw Data into Body Fat Estimates
The raw millimeter measurements collected from the various anatomical sites must be converted into an estimated body fat percentage using mathematical models known as predictive equations. These equations establish a relationship between the sum of the skinfold thicknesses and a calculated body density. Popular equations, such as the Jackson and Pollock or Durnin and Womersley models, often use the sum of three, four, or seven different site measurements. These formulas are population-specific, meaning they were developed and validated on groups of people with similar characteristics, and they often require input variables like age and sex to improve the accuracy of the estimate.
Once the body density is estimated, it is then converted into a percentage of body fat using a secondary formula, most commonly the Siri equation. This equation assumes a constant density for fat mass and fat-free mass, which is a conceptual limitation of the method. The conversion process involves multiple steps of calculation, which is why the raw skinfold measurements are sometimes used simply as a direct index of regional fatness without conversion.
Accessibility and Accuracy of the Method
Skinfold measurement remains relevant in health and fitness due to its practical advantages, including low cost, portability of the calipers, and the speed of measurement. Compared to high-cost methods like Dual-Energy X-ray Absorptiometry (DEXA) or hydrostatic weighing, skinfolds are highly accessible. However, the accuracy of the resulting body fat percentage is highly dependent on two main factors: the skill of the administrator and the appropriateness of the predictive equation used.
The method is considered to have a prediction error ranging from approximately 3% to 5% when compared to criterion methods. Skinfolds tend to be less accurate for individuals who are extremely lean or who have high levels of obesity, as the physical pinch becomes more difficult to standardize. Despite these limitations, the skinfold method is excellent for tracking individual progress because repeated measurements, when performed by the same skilled technician, offer high reliability and consistency over time.