Anthropometrics / Body composition Flashcards
What is anthropometry?
The science that deals with the measurement of size, weight, and proportions of the body. Examples include BMI, somatotyping, and waist/hip ratios
What is weight bias?
The active or passive formation of unreasonable judgments based on a person’s weight. This can be based on false preconceived notions
What is stigma in the context of weight?
The social implication carried by a person who is a victim of prejudice and weight bias.
What are the Beliefs About Obese Persons Scale (BAOP) and the Attitudes Towards Obese Persons Scale (ATOPS)?
Tools used to assess one’s own potential weight bias
What are some tools to help with assessing individuals with excess weight?
These include a private space for assessments, large-size gowns, sturdy armless chairs, large and extra-large blood pressure cuffs, and a wide-based scale that measures > 350 pounds
What are some best practices when assessing individuals with excess weight?
Be prepared to avoid awkward moments, ensure weighing takes place in a private location, record weight without judgment, and offer the choice of not seeing the results
When should skinfolds be avoided in an assessment?
If an individual has a BMI greater than 30 (classified as obese), skinfolds should not be included in the assessment
How is height measured, and what units are used?
Height is measured using a stadiometer to the nearest 0.5 cm. Conversions: 1 cm = 0.394 inches, 1 inch = 2.54 cm, 1 m = 3.28 feet, 1 foot = 30.5 cm
How is weight measured, and what units are used?
Weight is measured using a calibrated scale to the nearest 0.1 kg. Conversions: 1 kg = 2.20 pounds, 1 pound = 0.454 kg, 1 g = 0.035 oz, 1 oz = 28 grams.
What is Body Mass Index (BMI)?
- Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women
- BMI is calculated as body mass (kg) / height (m²).
- It’s reasonable for health screening and large populations.
- It was originally conceived by Adolphe Quetelet
What are the BMI classifications?
Normal range 18.50-24.99
Is BMI a diagnostic tool?
No, BMI should be used as a screening tool, but not as a diagnostic criteria for overweight and obesity
What is waist circumference used for?
Waist circumference is used to assess health risk and is adopted by CSEP and Clinical Practice Guidelines
What is the cutoff for waist circumference?
Men: greater than or equal to 102 cm
Women: Greater than or equal to 88 cm
Why are formulas to predict % body fat from circumferences not recommended?
Because they are regression equations based on cadaver analysis and they are not one size fits all
What is the clinical significance of subcutaneous fat?
Subcutaneous fat is not as metabolically damaging
What are Z-scores and percentiles used for?
Z-scores indicate how many standard deviations a value is from the mean, and percentiles represent where a value places with respect to the entire distribution. Both are useful for identifying relationship to a cohort (i.e. same age)
What are some important considerations when measuring circumferences?
Careful measurement of bony landmarks, consistent technique to not compress the circumference, and frequent inspection of the tape for stretch or wear are important
What is the focus of body composition?
Techniques to measure body fat and lean body mass or fat-free mass
What are the three categories of methods for measuring body composition?
- Direct (chemical or cadaver analysis),
- Indirect (laboratory-based, e.g., hydrostatic weighing, DEXA),
- Doubly Indirect (field-based, e.g., skinfolds, height/weight/circumference derivations)
What is the most common compartment model in body composition?
The two-compartment model, which divides the body into fat and fat-free mass
What are the assumed densities in a two-compartment model?
Fat has a density of 0.900 g/ml, and fat-free mass (FFM) has a density of 1.100 g/ml.
* Note FFM and LBM includes muscle, bone, organs etc
What are multiple compartment models?
Models that account for a greater number of body compartments, thus reducing error. An example is DEXA, which uses a three-compartment model
What is the principle behind hydrostatic weighing?
- Based on Archimedes’ Principle, which states that an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object.
- In simpler terms, whenever something is put into a liquid, it pushes some of that liquid away. The liquid then pushes back with a force that’s exactly as heavy as the water it moved. If this force is strong enough to counteract the object’s own weight, the object will float; if not, it will sink.
What information must be known to conduct hydrostatic weighing?
Residual volume (calculated based on height, age, sex), density of water (varies with temperature), trapped gas (GI approximated to be 100mL), dry body weight, and submerged body weight
How is residual volume calculated for men?
RV (L) = 0.019 * height (cm) + 0.0155 * age - 2.24
How is residual volume calculated for women?
RV (L) = 0.032 * height (cm) - 0.009 * age - 3.90
What is a possible discrepancy between different formulas for calculating % body fat from body density?
There can be a range of variability, with a potential ( ~5% absolute; 23% relative) discrepancy in results
What is a limitation of hydrostatic weighing related to the assumption of constant density of fat and LBM?
There is a possible 19% (relative) error in body fat prediction due to variability in the density of lean body mass in women.
What is a limitation of hydrostatic weighing related to the assumption of trapped air?
There is a possible 8% (relative) error in body fat prediction based on variability in lung volumes alone
What are some factors that can affect body mass determination in hydrostatic weighing?
Hydration/dehydration, and nutritional status can influence the calculation
How can the accuracy of hydrostatic weighing be enhanced?
By doing 9-10 trials
What is Air Displacement Plethysmography (BodPod)?
A method using air displacement, similar to hydrostatic weighing, but automated.
What are some considerations for BodPod?
Need to minimize air displacement, but not full expiration, and population-specific equations should be considered
What is DEXA?
Dual Energy X-Ray Absorptiometry, which uses a 3-compartment model (lean soft tissue, fat soft tissue, and bone) and low-level radiation to scan the whole body
DEXA is the gold standard
What are the limitations of DEXA?
Relatively expensive, need technical certification, cannot be used in some populations (pregnancy), has size limitations, and metallic implants/other radiological tests may interfere
What is Magnetic Resonance Imaging (MRI)?
method that also assumes a 3-compartment model and uses a high-frequency magnetic field to vibrate molecules. It can provide very fine spatial data and is considered the gold standard
What are the limitations of MRI?
Very expensive, limited accessibility, and has limitations with respect to the size of individuals
What are skinfolds?
A method that measures the thickness of fat folds including the skin at various anatomical sites around the body
- Doubly indirect measure
What are the major assumptions of using skinfolds?
The choice of sites are representative of total body fat, and subcutaneous fat is related to total body fat.
What are the sources of variability in skinfold measurements?
Type of caliper, jaw tension, landmarking of site, amount of fat pinched, time taken to read measurement, and number of sites/formula used
How does the type of caliper affect skinfold measurements?
A 10% difference between Harpenden vs. Lange calipers has been reported.
How can accuracy in skinfold measurements be enhanced?
By using consistent technique with respect to landmarking, amount of fat pinched, time taken to read measure, and finger pressure
How much can % fat from skinfolds vary?
Approximately ± 5 %, but is usually higher
What is a recommendation for skinfold measurements?
Use techniques that include upper and lower body skinfolds.
- How are skinfold measurements used to predict body fat?
- How equations for skinfolds generally work
The sum of skinfolds is directly entered into a formula that predicts % fat, or the sum is entered into a formula to predict body density, which can then be used to calculate % fat
What is the validity of skinfold measurements?
Correlations with UWW reported as high as r = 0.92. Note it is a doubly indirect method that reduces validity
What is the reliability of skinfold measurements?
Test retest reliability of r = 0.99, but dependent on technique
When is it recommended not to perform skinfolds on the general public?
When BMI is over 30
What is Bioelectrical Impedance Analysis (BIA)?
A non-invasive method using a low-level electrical current to measure impedance (opposition to current flow)
How does BIA work?
Tissues with more water (like muscle) have less impedance, while tissues with less water (like fat) have greater impedance
What are the pre-test guidelines for BIA?
assumptions/ pretest quidelines are questionnable
No eating or drinking within 4 hours, no exercise within 12 hours, must urinate within 30 minutes, no alcohol within 48 hours, no diuretic medications within 7 days, and no testing on certain days of the menstrual cycle
What is the validity and reliability of BIA?
Validity is questionable; reliability can be good under controlled conditions, with varied reported range of r = 0.66-0.94. Different manufacturers use different formulas
What is Near-Infrared Interactance?
A method that measures optical density of near-infrared light for the bicep of the dominant arm.
How does Near-Infrared Interactance work?
Fat absorbs light, and LBM reflects light. A sensor measures the difference between light emitted and reflected back. It uses formulas with assumptions to predict % fat, but can underestimate body fat up to 10%, especially in obese clients
What do CSEP CPT and AFLCA CFT recommend for evaluating anthropometrics?
BMI and waist circumference, as opposed to body composition
What are some key considerations when selecting a measurement technique?
Validity and reliability of technique, application with respect to performance or health, practicality and cost, and risk
What factors should be considered when selecting formula-based outcome measurements?
Population, age, sex, and if anthropometrics/body composition are dynamic based on population (children/pregnancy)
What is important when using measurements?
Consider normative data availability, report variability with measurement, ensure good technique, and do not succumb to technology without research support.
