Content by: Jaymee Dudley
You know you’ve got bones; you know you’ve got muscle and you know you’ve got fat. But have you ever wondered how much of each you have? Body composition is a way of describing what your body is made up of. By analysing your body composition, you can accurately detect changes in your body fat and muscle mass.
So many people jump on the scales and are not happy with the number they see. They then head out to complete an 8-week challenge, expecting to shed those unwanted kilos, only to jump on the scales again and see an equal or higher number. I’m sure a few sour words will be muttered along with the phrase; ‘these scales must be broken’. As a matter of fact, the scales are perfectly fine, however it has not been taken into consideration that muscle weighs more than fat! Throughout these 8-week challenges, your body composition will change as the workouts will burn fat but also increase muscle mass. Assessing your body composition rather than just your weight will allow you to notice the small differences that are not so obvious with the naked eye.
There are several ways to measure and assess body composition, however some are more accessible and ready to use than others. When assessing body composition, it is important to note that for the best results, assessment should be conducted at the same time of day, on the same machine and in the same setting. Assessment should not occur immediately after exercise, food or sleep.
The most common and well-known methods to measure body composition include:
This method uses callipers to measure skinfold thickness at various sites on the body in order to estimate total body fat. Measuring skin folds can be quite an invasive method as the ‘tester’ will have to physically hold the folds of skin before using the callipers to pinch the skin. This method sounds quite simple and getting your hands on a set of skinfold callipers can be quite easy, however it is important to ensure that they are calibrated and used following a standardized procedure as there are many anatomical locations that can be measured.
This method is based on the Archimedes Principle which states that “the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object”. In layman’s terms, muscle sinks and fat floats, so someone with more body fat will weigh less when submerged in water, whereas someone with more muscle will weigh more when submerged in water. During measurement, an individual will be first be weighed on dry land. Following this, they will get into a large tank of water, sit on a special scale, be fully submerged into the water, be asked to expel all air from their lungs and will then be weighed underwater. This is repeated 3 times. A special calculation is then used to calculate lean weight and fat weight.
Dual-energy X-ray Absorptiometry (DXA)
This method was originally designed for the diagnosis of osteoporosis and whilst it is still used for this, it is also one of the most widely accepted laboratory-based methods for assessing body composition. The technology is “based on the differential attenuation of transmitted photons at two energy levels by bone, fat and lean tissue” – Mazess et al. 1990. Put simpler, the machine sends a small beam of low-dose x-rays through the body with two distinct energy peaks, with one peak mainly absorbed by soft tissue and the other by bone. The results are expressed as a ratio, which is specific to different molecular components, including fatty acids, protein and bone. Whilst the individual is exposed to very small amounts of radiation through the x-ray, DXA is safe to be used multiple times for monitoring. However, individuals are cautioned against taking more than four scans per year due to the collective radiation dose and those who are pregnant should not be scanned.
Bioelectrical Impedance Analysis (BIA)
This method has become increasingly popular due to ease of access, cost-effectiveness and portability. During measurement, a small electronic current will be passed through the body at different frequencies to assess body composition based on the conductivity of fat mass (FM) and fat free mass (FFM). FFM will contain water and electrolytes, therefore making it a good electrical conductor. FM on the other hand is the opposite and will not conduct the current effectively. BIA machines with higher frequencies provide more accurate results due to the ability of the higher frequencies to pass through cell walls. Most BIA machines will be able to identify body fat % and mass, muscle mass, bone mass and total body water amongst other results. As BIA uses an electrical current, individuals with pacemakers or any other mechanical implants SHOULD NOT use this method and those who are pregnant or have allergies to metals should consult their doctor before use.
So whether you feel you’re made up of slugs, snails and puppy dog tails or sugar, spice and all things nice, assessment of your body composition will help you identify what you’re made of and provide you with so much more than just your body weight.