‘Have I lost weight?’ Or for some people the question may be ‘Have I made gains in muscle mass?’. These are common question asked by gym goers. But perhaps they are not the right questions. Instead ask yourself ‘has my body composition changed?’.
Yep it’s true, muscle weighs more than fat but if the scales go up this doesn’t mean you can use the throwaway line ‘must be because I’ve put on muscle’. You may have made the weight gain you planned but is it because of increased fat mass or lean muscle mass? Equally, your body weight may drop if you muscle mass drops but that’s no good if your fat mass has stayed the same.
Here at Warwick Workout one of our pillars of excellence is the need for measurement integrity. If you can measure it well then you can be confident that you have improved. If you can measure it well you can make decisions about your program and what needs to be adjusted to make improvements.
The aim of this article is to help guide you through the maze of potential measures out there so that you can make an informed decision on how you will track changes in your body composition. Before we go into pros and cons of different measures we need to understand two key terms:
- Reliability – if you perform the same test two days in a row (replicating all conditions: food, sleep, time of day, fluid intake, exercise) does it give you the same scores? E.g. within 5%.
- Validity – Does the test measure what you want to find out relative to a gold standard? For example, your scales may be reliable, (giving you the same score between days) but they may not be valid as they measure you 5 kg heavier than you actual weight.
Any body composition test you use needs to be valid (measuring what it’s supposed to) and reliable (if conditions don’t change the test should consistently give the same score). We’re going to use these terms as we explore the pros and cons of various ways of assessing body composition.
Skinfold measurement requires the measurement of folds of skin using callipers. Typically, 6 to 8 sites are used across the body. These scores are added up to give a score in millimetres. This score can be translated using a formula to predicted percentage body fat (note that there are an abundance of these formulas). However, prediction of percentage body fat from total skinfolds can confound error and so it is recommended that you use the total skinfold score in millimetres. A key assumption of skinfolds is that subcutaneous fat (just under the skin) is directly related to amounts of visceral fat (fat around the organs).
• Relatively cheap (we charge $20 at Warwick Workout).
• Relatively quick (15 minutes).
• Gives a whole-body picture of fat and the areas where you may have the highest deposits.
• Needs to be performed by an accredited tester to ensure high reliability (typically 5%).
• Can feel invasive as your body needs to be marked up and skinfolds pinched.
This is a body scan that is a form of X-ray using a very small amount of radiation. Originally designed to measure bone mineral density, Duel X-ray absorptiometry uses calibrated X-ray beams to determine between bone tissue and soft tissue.
• Non-invasive and quick as you lie on a platform for 5 minutes.
• Minimal operator error.
• Measurement minimally affected by hydration level.
• High reliability (1-2%).
• Low level radiation used.
• Expensive ($150-200) per scan.
BIOELECTRICAL IMPEDANCE (BODY SCANS)
Bioelectrical impedance was originally developed to assess hydration status in military personal. Bioelectrical impedance passes a small electric current through the body, often by holding two handles or stepping barefoot onto the device. The electrical current will pass through the body compartment with the least resistance, which is water. This process results in an estimate of total body water which, in turn, is used in an formula to predict body fat percentage with the addition of body weight, height and age.
• Quick and non-invasive as it requires the person to stand and hold a device.
• Relatively cheap.
• An underlying assumption of bioelectrical impedance is that body shape does not change, which, of course is often the aim of a gym program.
• Reliability of this measure can be poor (>10%) and is often dependent on choosing the best formula (of which there are 100s) to translate the electrical conductively measure into an estimate of percentage body fat.
• As the body fat percentage estimate is highly dependent on hydration status, it is important to perform the measure at the same time each day (e.g. first thing in the morning).
If you would like to book a skinfold assessment please get in touch.
by Laurence Houghton PhD, High Performance Coach, Warwick Workout.
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