Different methods of determining an individuals body composition
Skinfold callipers
Skinfold callipers is one of the cheapest and quickest ways of estimating body fat percentage. To perform this test a professional must place their index finger and thumb about 3 inches away from each other over various parts of the body, the fingers are then pinched together holding onto the skin and subcutaneous fat, it is critical not to pinch onto the muscle, clamp the skinfold callipers around the area about 1cm below your fingers, make sure they are parallel with the area you are measuring, record the results shown on the skinfold callipers which will be displayed in millimetres. Typically the measurements are all taken from the right side of the body. To estimate body fat percentage a 3 or 7-site method is typically used, the 7-site method is more reliable but the 3-site method is quicker. The 3-site method is taken from the chest, abdomen and thigh, whilst the 7-site method is taken from the triceps, chest, abdomen, thigh, subscapular, suprailiac and midaxillary. It is best to take 3 measurements at each site and then take the average. Add up the results from each site and you can use a chart to see what body fat percentage you are for your age range.
The chart to gauge body fat percentage for the 3-site method:
There are many downsides with skinfold callipers, one is that it doesn’t account for different patterning of subcutaneous fat around the body and thickness of the skin. This is why the 7-site method is more reliable than the 3-site method as it takes measurements from more points around the body. The use of skinfold callipers heavily relies on the quality of the callipers and the tester's ability to use them, expensive, high-quality callipers combined with a competent and experienced practitioner is more likely to give you reliable results, whilst cheap, poor-quality callipers combined with an inexperienced practitioner is more likely to give you unreliable results.
Magnetic resonance imaging (MRI)
The MRI requires an individual to lay flat on a motorized bed which is then moved into a large cylindrical scanner which is open at both ends. The MRI creates a magnetic field which causes all the spinning protons in our body to align with the magnetic field, the stronger this magnetic field the more detailed the image will be, radio waves are then sent through the body and it’s weak magnetic field disrupts the protons and they gain energy, the radio waves are then turned off and the protons go back into alignment with the magnetic field, this releases energy, a coil is placed around the particular body part and it measures the emitted energy, from this a computer image of the cross-sectional area of the scanned body part is generated, as different tissues contain different amounts of water, and each water molecule contains 2 protons which release the energy, so the types of tissue in the scanned area can be gathered. This process takes 15-90 minutes. Sometimes an individual may need a contrast dye to be able to enhance the differences between tissues, this can be injected, drank or enter the body through an enema before the test.
MRI of the thigh:
The MRI is noninvasive, it doesn’t produce any ionising radiation and it is a very accurate method for judging body composition, and this is why the other methods of judging body composition are usually judged in comparison to the MRI, as it often estimates muscle mass correctly within 7.5%. However, getting an MRI scan is expensive, time-consuming and the accuracy of the MRI can be compromised when trying to gather information on muscles in close proximity of others or for muscles with multiple heads, for this reason, the volume for smaller muscles is often underestimated, likely due to a lack of samples taken along the muscles. Muscles with a large ratio of surface area to volume are particularly hard to judge the muscle mass of. An MRI can be used to take samples all around the body and find an individual’s whole-muscle volume, but the MRI is best used to find the muscle volume of certain body parts.
Computerized tomography (CT)
The CT scan requires an individual to lie on a table, and an X-ray rotates around the whole body or the part of the body which the CT scan is wanted on, and X-rays are emitted into the body, because of this there is a small level of ionising radiation emitted which can potentially cause harm with frequent use. The emitted X-ray beams slow down when crossing different tissues and then are received by detectors to produce thin-sliced images, which are then processed to create clear images of the body. Sometimes an individual may need a contrast dye to be able to sharpen the differences between tissues, This can be injected, drank or enter the body through an enema before the test.
The CT scan is expensive and inconvenient, but it is a very reliable method for finding an individuals muscle mass, but not as much as an MRI as it often overestimates muscle mass by 10-20%, also, similar to the MRI, muscles that have close muscle bellies are particularly difficult to determine the muscle mass for.
Dual X-ray absorptiometry (DXA)/ Dual-energy X-ray absorptiometry (DEXA)
This method requires an individual to lie on a bed with a DXA machine over it, the machine moves over the body and sends low-dose X-rays through the body to assess the density of the body at different points, from here it can divide the body into lean mass, fat mass and bone mass, which is displayed on a computer. The scan lasts 3-7 minutes.
DXA scan of the whole body:
The DXA is reliable, convenient and relatively inexpensive compared to other similar methods. The DXA isn’t just used to determine muscle mass, it also can find the density of bones, and find the quantity of fat around the body, including visceral fat which increases the risk of metabolic diseases and injury. However, the DXA does emit very low levels of radiation, but this shouldn’t be a problem with infrequent usage. The DXA of course also requires a professional to operate the machine, making it impractical. Even though the DXA is usually a reliable method to find body composition it does depend on the type of unit used, whether this is a pencil-beam or a fan-beam unit, and the population the scan is performed on, there is also some evidence that food consumption of any kind increased DXA estimates of both total and regional soft-tissue mass by up to 3%, this promotes the idea that the DXA scan should be performed after an overnight fast, the DXA has also shown to be unreliable when tracking changes in muscle mass due to resistance training, this is likely due to changes in adipose tissue and skin mass which change the algorithm used by the DXA to estimate muscle mass.
The DXA also has the ability to estimate the lean mass of particular body parts, as well as the whole body, but the results seem to overestimate the lean mass in particular body parts for Caucasians. Finding the lean mass of particular body parts can be useful to find muscular imbalances which can affect balance and coordination increasing the risk of injury.
Bioelectrical impedance analysis (BIA)
The BIA requires an individual to stand on a scale where a low-level electrical current is sent through the body, and then body composition is estimated based on the ease of electrical flow through the body, the BIA does take into account the individual's height, weight and sex so this isn’t a problem. The BIA is very quick and convenient, as it only takes a few minutes to complete. It is also rather inexpensive.
Most BIA units exclusively measure the body composition of the whole body, but some can measure the composition of certain body parts, some can also calculate the intracellular and extracellular fluid compartments.
There are 2 kinds of BIA units, these are single-frequency units and multifrequency units. Single-frequency units only send one 50 kHz electrical impulse through the body, which can go through intracellular fluid, but also penetrates cell membranes, this makes single-frequency units an unreliable method of judging body composition. A multi-frequency unit sends an electrical impulse below 50 kHz through the body to find the quantity of extracellular water and it also sends an impulse of up to 1000 kHz which estimates total body water, from here intracellular water can be calculated. A multi-frequency unit is more reliable than a single-frequency unit for judging body composition.
Because BIA uses body fluids to estimate body composition it is highly susceptible to changes in results depending on hydration levels, this may be particularly problematic to females during different stages of their menstrual cycle. Hydration levels can also be significantly influenced by food consumption which makes an overnight fast necessary before the test. BIA has been shown to overestimate fat-free mass and it has been proven to be a fairly unreliable method of finding changes in muscle mass due to resistance training.
Different manufacturers of BIA machines have different methods of calculating body composition which explains differences in results between different kinds of units, they can vary significantly if they don’t take into account differences between populations. There are also different electrode configurations in different units which can send an electrical impulse from hand-to-hand, foot-to-foot and hand-to-foot, the hand-to-hand units measure the body composition of only the upper body, foot-to-foot units measure the body composition of only the lower body and hand-to-foot units are therefore the most accurate method for judging whole body composition.
A hand-to-foot BIA machine:
Tape measure
Using a tape measure to find the girth of certain parts of the body is a quick and easy method to estimate an individual's body composition, it also has been proven to be more reliable than skinfold callipers. Unfortunately using a tape measure can only measure the girth of a general area of the body making finding measurements for particular muscles difficult, for example, trying to find the size of the biceps by using a tape measure to find the girth of the upper arm will be cofounded by the triceps. Another problem with the tape measure is that it can’t distinguish between types of tissue so an increase in the girth of a body part may be due to an increase in fat, skin thickness or intracellular and extracellular water content rather than muscle. Using a tape measure to find information on an individual’s body composition also heavily relies on the practitioner’s ability to get the measurements, they must be able to keep the tape measure at the desired level of tightness around the body part and it must always be on the same position on the body so it can be compared to other individuals results or the pass results of the person performing the test.
Muscle biopsy
A muscle biopsy is performed when an incision is made in the skin then a needle is inserted into the site and a small amount of muscle tissue is extracted. The tissue is then cut into thin slices and analysed under a microscope, a technique can be applied to stain the muscle tissue in order to distinguish the different fibre types. Muscle biopsies can also be used to analyse different protein subfractions, such as sarcoplasmic and contractile proteins.
A muscle biopsy gives a unique insight into an individual’s muscles but it does have some downsides. The muscle biopsy can cause some pain in individuals, even though anaesthetics are administered to the site which has the biopsy performed on it. The muscle biopsy also only extracts 100mg of muscle tissue, which may not give an accurate representation of the entire muscle depending on where the biopsy is taken from along the length of the muscle or even how deep the biopsy is taken in the muscle, as type I muscle fibres and larger muscle fibres typically reside deep in the muscle and type II fibres typically reside more superficially, this is because there is a better blood supply deep in the muscle. This makes the muscle biopsy an unreliable method to measure muscle growth, but it can be insightful when combined with other methods.
Muscle biopsy:
Hydrodensitometry
To perform a hydrodensitomety an individual is weighed on scales and is then dunked into a water tank and weighed under water. Archimede’s principle is then used which states that the amount of water displaced from the tank is equivalent to whatever the volume is of the object put in the tank. As fat is less dense than water and lean tissue is more dense than water an individual with a lower body fat percentage will weigh more underwater than an individual with a higher body fat percentage, providing that they both weighed the same on land. The mass of the individual can be divided by their volume to determine their density. From here an individual's fat mass can be estimated, the equations used for these estimations are most often determined by findings found in white male and female cadavers, and this may make the results unreliable in certain populations. Premenopausal women’s results can vary substantially through different phases of their cycle, likely due to changes in water weight, women should therefore perform the test at the same stage of their cycle if they want to compare results.
Hydrodensitomety is relatively inexpensive, but it is also inconvenient. Even though hydrodensitometry is typically very reliable, there are also many potential sources of error. If the performer fidgets in the tank it can affect the results, they, therefore, must remain calm and still, it is also important for the performer to maximally exhale when underwater as the air in their lungs affects their buoyancy, this can fill very unnatural and uncomfortable, even if the performer does maximally exhale underwater they still need to account for residual volume, which is the amount of air remaining in the lungs after a maximal exhalation, this can vary by about 600ml between different individuals, this can affect measurements by up to 8%, especially in larger individuals.
Someone performing a hydrodensitometry:
Air displacement plethysmography (ADP)
To perform an air displacement plethysmography the individual sits motionless in an egg-shaped, fibreglass unit, known as a bod pod for about 10 minutes, the test uses air displacement and the pressure-volume relationship to estimate body volume, from here estimations on fat mass can be made.
The ADP is simple and easy to perform, but it is also expensive and there are certain factors which can make the test rather unreliable. The volume of the individual is affected by body temperature, hair, moisture and clothing, it is, therefore, better if they shave body hair and facial hair beforehand and wear a scalp cap for their head hair and a tight-fitting swimsuit. The seating position also can affect volume to a small degree, so it is important for the performer to sit in a well-postured and relaxed position. Physical activity and fluid and food intake must be restricted leading up to the test as this will affect the results. The room temperature can also significantly affect results, so room temperature should remain at a fixed level. ADP appears to be reliable in lean individuals but appears unreliable in overweight individuals.
Someone performing an air displacement plethysmography:
Ultrasound
An ultrasound is performed when a transducer, coated in a gel, is placed over a particular muscle of interest and emits sound waves which pass through bodily tissues, these waves are partially reflected back to the transducer to display an image. When the image depicts what the sonographer wants they freeze the image and take the desired measurements. The ultrasound has two modes, A-mode (amplitude modulation) and B-mode (brightness modulation). The A-mode emits narrow sound beams to scan tissue discontinuity and produce spikes on a graph to determine muscle morphology, but the reliability of this is not well known. B-mode can produce images of muscle thickness or cross-sectional area at a particular section of the muscle, this way the ultrasound can find information about regional-specific hypertrophy. Equations can be applied from the ultrasound images, which take into account muscle thickness and limb length, to estimate muscle volume, and results from this seem to be reliable when compared to the MRI, however, as regional specific differences occur with resistance training it may not be a great technique for measuring muscle hypertrophy. An extended field-of-view ultrasound is when the sonographer moves the transducer along the muscle at a fixed speed to produce one long, high-quality image of the cross-sectional area of the muscle, the computer then can generate a 2D panoramic image. 3D imaging may be an effective method for estimating muscle volume in the future.
This method is safe, quick and inexpensive. There are some potentials for error however, the results heavily depend on the skill of the sonographer, as if they apply too much pressure to the muscle it can significantly affect the results. It is easier to obtain reliable results from those with a low body fat percentage than a high one, it is also easier to obtain results in certain muscles than others, for example, the posterior thigh is more difficult to get results from than the anterior thigh, possibly due to the shape of the femur. Changes in muscle size may be awkward to track as scans may be taken at different sites along the muscle.
Biochemical methods
There are many biomechanical methods used to estimate muscle mass, and even though it’s not a very popular option currently it may be in the future. The most popular biochemical method involves monitoring urinary creatinine excretion over 24 hours. This method has stemmed from animal studies showing a linear relationship between creatinine excretion and skeletal muscle mass. Creatinine is a waste product of creatine when it is used in muscles, and this method assumes that the creatine conversion to creatinine rate is equal between individuals for a particular amount of muscle, which is not true for resistance trained individuals but it may be more reliable to sedentary individuals. This test also heavily relies on accurate urine collection and a stable protein intake which can affect the results, as a large amount of protein consumption in one meal has been proven to increase creatine levels, at least temporarily.
One of the best biochemical methods is the D3 -creatine dilution method. This method requires the participant to drink D3 -creatine in water which is taken up almost exclusively by skeletal muscle. The quantity of D3 -creatine in the urine can then be found via chromatography-tandem and estimations of skeletal muscle mass can be made. So far this method has been proven to be very reliable in rodents, and with the very limited research in humans, it does still seem like a reliable method of determining muscle mass, although it does tend to underestimate muscle mass and the variability between individuals was very large when compared to MRI measurements, especially for women. The D3 -creatine dilution method may also struggle to measure changes in muscle mass due to resistance training as this will affect creatine usage in the muscles.
Disclaimer: use the information provided in this article at your own risk, as I will not be liable for any harm that may be caused by it.
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