Skinfold Measurements: Sites, Protocols, and Best Practices

Where do you take skin folds?

Skinfold measurements are taken at specific anatomical sites across the body to estimate subcutaneous fat, which is then used to calculate total body fat percentage. Common sites include the triceps, subscapular, suprailiac, abdominal, thigh, and chest.

Understanding Skinfold Measurements

Skinfold measurements represent a widely used, practical, and non-invasive method for estimating body composition, specifically body fat percentage. The underlying principle is that a significant proportion of the body's total fat stores are located directly beneath the skin (subcutaneous fat). By measuring the thickness of these folds at various standardized sites, and applying population-specific regression equations, one can derive an estimate of total body fat. This method is valuable for tracking changes in body composition over time, assessing health risks, and guiding fitness and nutrition interventions.

Key Anatomical Sites for Measurement

To ensure accuracy and comparability, skinfold measurements are consistently taken at precise anatomical landmarks. The specific sites chosen often depend on the prediction equation being used (e.g., 3-site, 7-site protocols). Here are the most common and standardized locations:

• Triceps: This measurement is taken on the posterior midline of the upper arm, halfway between the acromion process (bony point of the shoulder) and the olecranon process (bony point of the elbow). The arm should hang relaxed. A vertical fold is typically used.
• Biceps: Located on the anterior midline of the upper arm, directly above the cubital fossa (elbow crease), at the same horizontal level as the triceps site. A vertical fold is taken.
• Subscapular: This site is found just inferior to the inferior angle of the scapula (shoulder blade). The fold is taken diagonally, running from the superomedial to the inferolateral aspect.
• Suprailiac: Positioned on the midaxillary line (line extending down from the middle of the armpit), directly above the iliac crest (top of the hip bone). The fold is taken diagonally, following the natural crease of the skin.
• Abdominal: This measurement is taken 2 centimeters (approximately 1 inch) lateral to the umbilicus (belly button), usually on the right side of the body. A vertical fold is grasped.
• Thigh: Located on the anterior midline of the thigh, midway between the inguinal crease (where the thigh meets the torso) and the proximal border of the patella (top of the kneecap). The subject should be standing with weight evenly distributed or seated with the knee flexed at 90 degrees. A vertical fold is taken.
• Chest (Pectoral):
  • Men: Midway between the anterior axillary line (front of the armpit) and the nipple. A diagonal fold is taken.
  • Women: One-third of the distance between the anterior axillary line and the nipple. A diagonal fold is taken.
• Midaxillary: At the level of the xiphoid process (bottom tip of the sternum), along the midaxillary line. A vertical fold is taken.
• Calf: On the medial (inner) aspect of the calf, at the maximal circumference. The subject places their foot on a box or chair with the knee flexed at 90 degrees. A vertical fold is taken.

Common Measurement Protocols

While individual sites are measured, they are typically combined into multi-site prediction equations to estimate overall body fat percentage. Some widely used protocols include:

• 3-Site Protocols (Jackson & Pollock):
  • Men: Chest, Abdomen, Thigh
  • Women: Triceps, Suprailiac, Thigh
• 7-Site Protocol (Jackson & Pollock): Chest, Midaxillary, Triceps, Subscapular, Abdominal, Suprailiac, Thigh. This protocol is considered more comprehensive.
• 4-Site Protocol (Durnin-Womersley): Triceps, Biceps, Subscapular, Suprailiac.

Each protocol utilizes specific regression equations derived from research on various populations.

The Measurement Procedure

Regardless of the specific site, the general procedure for taking a skinfold measurement involves:

1. Site Identification: Accurately locate the anatomical landmark.
2. Pinch the Fold: Use the thumb and forefinger of one hand to firmly grasp a double layer of skin and subcutaneous fat. The pinch should be about 1 cm (0.4 inches) above the site where the calipers will be placed, ensuring the muscle is not included.
3. Apply Calipers: Place the caliper jaws perpendicular to the fold, midway between the crest and base of the fold.
4. Read Measurement: Release the caliper grip slowly, allowing the jaws to exert full pressure. Read the measurement (in millimeters) approximately 1-2 seconds after the grip is released.
5. Repeat: Take at least two, and ideally three, measurements at each site. If measurements differ by more than 1-2 mm, re-measure. Average the closest two readings.
6. Consistency: All measurements should be taken on the same side of the body (typically the right side) to maintain consistency.

Accuracy, Limitations, and Best Practices

While skinfold measurements are practical, their accuracy is influenced by several factors:

• Operator Skill: This is the most significant factor. Highly trained and experienced technicians are crucial for reliable results.
• Calipers: Different types of calipers (e.g., Harpenden, Lange, plastic budget calipers) can yield slightly different readings. Calibration is also important.
• Hydration Status: Dehydration can affect skinfold thickness.
• Time of Day: Measurements should ideally be taken at the same time of day for consistent tracking.
• Population Specificity: The prediction equations used are often derived from specific populations (e.g., age, gender, ethnicity). Using an equation on a population different from its origin can introduce error.
• Limitations: Skinfolds primarily measure subcutaneous fat and do not directly account for visceral fat (fat around organs), which is metabolically significant. They can be less accurate for extremely lean or very obese individuals.

For the most reliable results, it is essential to:

• Use a standardized protocol.
• Have the same trained individual perform all measurements.
• Track trends over time rather than relying on a single absolute value.

Who Should Perform Skinfold Measurements?

Due to the critical role of technique in accuracy, skinfold measurements should be performed by qualified and experienced professionals. This includes certified personal trainers, exercise physiologists, kinesiologists, registered dietitians, or other healthcare professionals who have received specific training in anthropometric measurement techniques. Proper training ensures precise site identification, consistent fold grasping, and accurate caliper application, leading to more reliable body composition assessments.