What Is an InBody Scan? A Plain Guide to Body Composition Testing
An InBody scan is a body composition test. You stand barefoot on a platform and hold two handles while the machine passes a very small, painless electrical current through your body, then estimates how much of your weight is muscle, fat and water, and how that is distributed between your arms, legs and trunk. It takes about a minute. The method is called bioelectrical impedance analysis, or BIA. It is not a medical scan and it does not produce an image, but used consistently it is one of the more practical ways to see whether training is changing what you are made of, not just what you weigh.
How the machine actually works
Different tissues conduct electricity differently. Muscle holds a lot of water and conducts well. Fat holds little water and resists the current more. By measuring that resistance, called impedance, the machine works out how much water is in your body and, from that, estimates lean mass and fat mass.
A few details set InBody devices apart from a typical bathroom scale with a body fat reading:
- Eight contact points. Two under each foot and two on each hand. A bathroom scale only measures through the feet, so it effectively guesses about your upper body.
- Segmental measurement. The body is treated as five sections: each arm, each leg and the trunk. That is how the printout can show, for example, that your left leg carries a little less lean mass than your right.
- Several frequencies. Low and high frequency currents travel through the body differently, which helps separate water inside the cells from water outside them.
The current is tiny and you will not feel it. What you do feel is the cold metal and the slightly odd stance, arms held away from your sides.
What a scan tells you
A standard printout runs to one page and includes these main measures. Our separate post on reading your InBody results line by line goes through each one properly; this is the overview.
| Measure | What it means in practice |
|---|---|
| Weight | Total body weight, as on any scale |
| Skeletal muscle mass | An estimate of the muscle you can train. The number most people want to see rise |
| Body fat mass and percentage | How much of your weight is fat, in kilograms and as a proportion |
| Total body water | Useful mainly for interpreting the other numbers and spotting an off day |
| Segmental lean mass | Lean tissue in each limb and the trunk, handy for spotting imbalances |
| Visceral fat level | An estimate of fat stored around the organs, given as a level rather than a weight |
Why weight alone misleads
The main reason to use body composition testing at all is that the scales cannot tell you why your weight moved. Two people can each lose two kilograms in a month. One has lost mostly fat and kept their muscle. The other has lost a worrying share of muscle because they cut food hard and stopped lifting. Their bathroom scales show the same number.
The opposite case is common with people who start strength training. Weight barely moves for several weeks, they become discouraged, and yet a scan shows a modest fall in fat and a modest rise in muscle. That is called body recomposition, and it is exactly the kind of progress weight alone hides.
How accurate is it?
Honest answer: accurate enough to track trends, not precise enough to treat any single number as fact.
BIA devices estimate. They do not measure fat directly. The reading depends on how much water you are carrying, and that changes with food, drink, exercise, alcohol, heat and, for women, the menstrual cycle. A large meal, a hard session or a night out the evening before can shift the result noticeably without any real change in tissue.
That has two practical consequences:
- Compare like with like. Scan at the same time of day, in a similar state, on the same machine. Your second scan is only meaningful against your first if the conditions match. Our guide to preparing for an InBody scan sets out the routine.
- Look at direction over several scans. A single shift of half a kilogram of muscle means little. Three scans over three months moving the same way means a lot more.
Methods such as DEXA, a low-dose X-ray scan used in clinical and research settings, are generally regarded as more precise for body composition, but they are less convenient and are not something you would do every few weeks. For tracking training, a consistent InBody routine is a sensible tool.
What happens during a scan in our studio
- You take off shoes and socks, and anything metal you can easily remove such as a watch.
- I enter your age, height and sex, which the machine uses in its calculations.
- You step onto the footplates, lining your heels and forefeet up with the electrodes.
- You hold the handles with your thumbs and fingers on the contact points, arms slightly away from the body.
- You stand still for around a minute while it measures.
- We go through the printout together and note the two or three numbers that matter for your goal.
The scan is optional. Some people want a baseline on day one; others prefer to wait a few weeks until they have settled into training. Both are fine.
Who should not be scanned
InBody advises that people with a pacemaker or another implanted electronic medical device should not use the scanner, because of the electrical current. During pregnancy the readings are not a useful measure of training progress, so there is little reason to scan. If you have any implanted device or a medical condition you are unsure about, tell me before the session and ask your GP or specialist if in doubt. If you have not exercised for a long time or have a heart condition, check with your GP before starting a training programme too, whether or not you are scanned.
How we use it in training
The scanner is part of the kit in the private training studio at The Highgate House, and it is there to inform coaching, not to grade you. In practice it does three useful jobs:
- Setting a baseline so we are not guessing at where you started.
- Checking a fat loss phase is costing fat, not muscle. If muscle mass is dropping, we look at protein, training volume and the size of your calorie deficit.
- Reassuring people when the scales stall. A flat weight with falling fat is good news, and it is much easier to keep going when you can see it.
I usually suggest a scan every four to eight weeks. More often than that, normal day-to-day fluctuation tends to drown out real change.
For broader context on healthy weight and body fat, the NHS BMI guidance explains why BMI is a starting point and why waist size and other measures are also worth considering.
Questions we get asked
Does an InBody scan hurt or feel like anything?
No. The current is far too small to feel. The only sensation is cold metal under your feet and hands.
Is it the same as the body fat reading on my bathroom scales?
Same basic principle, but an InBody measures through hands and feet, at several frequencies, segment by segment, so it is far less of a guess about your upper body. The readings from the two will rarely match.
How long does it take?
About a minute on the platform and five to ten minutes in total if we go through the results together.
Can I have a scan without personal training?
The scanner is used as part of coached sessions in the studio. If you want to understand how those sessions run, see our page on personal training in Highgate.
Book with The Highgate House
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The Highgate House, Archway Road, Highgate, London N6.
