How to use an InBody result to bulk, maintain or cut
An InBody result sheet gives body fat percentage and skeletal muscle mass, each against a standard band for your height and sex. No study turns those two numbers into a single bulk-or-cut rule. ArchiFit uses a simple one: high body fat means cut first, muscle above standard with normal fat means maintain, and anything else means build muscle.
Published Last updated By ArchiFit
What do body fat percentage and skeletal muscle mass mean?
Body fat percentage is the share of your body weight that is fat. Skeletal muscle mass is the weight of the muscles attached to your skeleton, the ones training builds. An InBody sheet shows each as a bar against a standard band for your height and sex. These are the bands ArchiFit works with:
| Measure | Men | Women |
|---|---|---|
| Body fat percentage, standard band | 10–20% | 18–28% |
| Skeletal muscle mass, standard band | 90–110% of a standard worked out from height and sex | |
What body fat percentage counts as high?
There is no single answer. The World Health Organization's 1995 definition of obesity used 25% for men and 35% for women. The American Society of Bariatric Physicians used 25% and 30% in its 2009 guidelines, as reported by Shah and Braverman (2012). The same authors note that body fat cut-points, like BMI, are arbitrary. ArchiFit uses the 25% and 30% lines to recommend losing body fat first.
How accurate is an InBody result?
InBody devices use bioelectrical impedance analysis (BIA), which estimates body composition from how a small current passes through the body. It is useful, with known limits:
- BIA "works well in healthy subjects and in patients with stable water and electrolytes balance", and follow-up measurements "must be interpreted with caution" (Kyle et al., 2004).
- In trained athletes, small fluid changes were read as changes in body fat. Measured body fat went from 14.4% to 12.3% after dehydration and to 15.5% after rehydration (Saunders et al., 1998).
- Compared with DXA scans, several InBody models showed small individual error but a systematic bias. They tended to underestimate body fat and overestimate fat-free mass (McLester et al., 2020).
- A review argued that impedance errors are not very different from those of so-called gold-standard methods (Ward, 2019).
Because hydration moves the numbers, compare readings taken under similar conditions, such as the same time of day, and read the trend across several sheets rather than one result.
Bulk, maintain or cut: a simple rule
ArchiFit applies these checks in order. They are ArchiFit's own rule, written to be easy to check against your sheet:
| If | Direction |
|---|---|
| Body fat is 25% or more (men) or 30% or more (women) | Lose body fat |
| Skeletal muscle is above its standard band, and body fat is not above its band | Keep current body |
| Anything else | Build muscle |
Example from the app: body fat 21% (below the 25% line) and skeletal muscle 31.8 kg, or 70.1 lb (within its band), gives build muscle. Body fat between the top of the standard band and the 25% or 30% line also gets build muscle. ArchiFit's reasoning is arithmetic: muscle added at the same fat mass lowers the body fat percentage.
Can you build muscle and lose fat at the same time?
Yes, even when already trained. A review found "a substantial amount of literature" showing body recomposition in resistance-trained people. It named two key factors: progressive resistance training and evidence-based nutrition (Barakat et al., 2020). ArchiFit's rule reflects the same idea by sending the middle ground to build muscle rather than to a separate bulk or cut.
How fast should you cut to keep muscle?
For natural bodybuilders preparing for a contest, a review recommends a calorie intake that loses about 0.5–1% of body weight per week to maximize muscle retention (Helms et al., 2014). On protein, a meta-analysis of supplementation studies found that total intakes above about 1.6 g per kg of body weight per day added no further muscle gain from training (Morton et al., 2018). Both studied specific groups, so check with a dietitian or doctor before changing your diet.
How ArchiFit reads an InBody sheet
- Take a photo of the sheet, pick a photo or PDF, or share it from the InBody app. The phone reads the text itself and deletes the photo. It is never sent to a server.
- The numbers show for a check before saving, and anything not read can be typed in.
- No sheet? Type the numbers in, or choose a plan without InBody by picking the direction yourself.
- With several results saved, weight, skeletal muscle mass and body fat changes sit on one screen.
See the full direction rule, rep ranges and splits, or progressive overload when you train alone.
General fitness information, not medical advice or a diagnosis. InBody is a trademark of InBody Co., Ltd.; ArchiFit is not affiliated with InBody.