Segmental analysis: five body regions, several different layers

A segmental result is not one “muscle map”. For each arm, leg and the trunk, it combines several views: lean mass, fat, water, water distribution and electrical phase angle. Only their relationship can show what may sit behind a difference between segments.

Where to find it: The Segmental Lean Analysis and Segmental Fat Analysis sections.

InBody results relationship guide

Read tissues first, then water and electrical context

Start with lean mass and fat, which address amount. Then check total water and ECW/TBW, and finish with phase angle. Right and left are always named from the measured person’s perspective.

01One body silhouette, five different questionsThe same regions recur across several sheets, but each layer uses a different quantity and a different comparison.
02Lean mass and fat do not use the same percentageKilograms show estimated amount in the segment. Percentages for segmental lean mass and fat compare against a reference rather than against each other.
03Water can change the lean-mass pictureMore water in a segment can raise estimated lean mass without the same increase in new tissue.
04Phase angle is electrical context, not a segment gradeSegmental phase angle is derived from resistance and reactance in the same body region and is reported at several frequencies.
05A side-to-side difference is an observation, not a diagnosisAsymmetry is more useful when checked across several layers and visits rather than inferred from one deviation.

One body silhouette, five different questions

The same regions recur across several sheets, but each layer uses a different quantity and a different comparison.

InBody divides the body into the right arm, left arm, trunk, right leg and left leg. For those five regions it can show lean mass and fat in kilograms, water in litres, ECW/TBW as a unitless ratio and phase angle in degrees. These values cannot be collapsed into one “segmental score”.

A practical reading order runs from tissue amount through water context to the electrical measure. If lean mass in one leg changes, for example, water and ECW/TBW help assess whether part of the difference may be short term. Phase angle adds another view but does not by itself establish segment quality or health.

Lean mass: modelled non-fat tissue amount.
Fat: estimated fat mass in the region.
Water and ECW/TBW: water amount and its relative distribution.
Phase angle: an electrical quantity, not a health score.

R armL armTrunkR legL leg

Muscle

Fat

Water

ECW/TBW

Phase angle

Teaching diagram — these are not your measured data.

Explained values

Lean mass by segmentSegmental Lean Analysis shows how much non-fat tissue — mostly muscle — falls to each of the five body parts: right arm, left arm, trunk, right leg and left leg.Fat by segmentSegmental fat shows how much fat mass falls to the right arm, left arm, trunk, right leg and left leg — in kilograms and as a percentage of the reference value for that segment.Water by segmentSegmental body water shows how many litres of water sit in each arm, in the trunk and in each leg separately.ECW Ratio by segmentECW/TBWThe segmental ECW Ratio shows what share of the water in each arm, in the trunk and in each leg sits outside the cells.Phase angle by segmentSegmental phase angle gives the phase angle separately for the right arm, left arm, trunk, right leg and left leg, at three frequencies: 5, 50 and 250 kHz.

Lean mass and fat do not use the same percentage

Kilograms show estimated amount in the segment. Percentages for segmental lean mass and fat compare against a reference rather than against each other.

Segmental lean mass has two views on the result: a comparison with the amount expected for ideal weight and an assessment of whether the segment is sufficient for the current body weight. Segmental fat instead shows kilograms and a percentage relative to the fat reference for that segment.

One hundred per cent is therefore neither the share of fat or muscle inside the arm nor a ceiling that must not be exceeded. When comparing sides, inspect kilograms, the type of percentage reference and the longer trend together. A small difference at one visit does not establish functional weakness or identify the cause of asymmetry.

Kilograms and percentages in segmental analysis are not interchangeable.
Segmental fat percentage is not the percentage of that segment’s own weight.
Lean mass is not identical to pure skeletal muscle mass.
For arm function, add a direct grip-strength measurement when available.

Explained values

Lean mass by segmentSegmental Lean Analysis shows how much non-fat tissue — mostly muscle — falls to each of the five body parts: right arm, left arm, trunk, right leg and left leg.Fat by segmentSegmental fat shows how much fat mass falls to the right arm, left arm, trunk, right leg and left leg — in kilograms and as a percentage of the reference value for that segment.Muscle massSMMSkeletal Muscle Mass is an estimate of the amount of voluntarily controlled muscle in kilograms — the muscle between bones and joints that produces movement.Fat massBFMBody Fat Mass is the amount of fat in kilograms — an absolute figure, unlike percent body fat, which is only a share of weight.

Water can change the lean-mass picture

More water in a segment can raise estimated lean mass without the same increase in new tissue.

Segmental body water shows litres in each body region. Segmental ECW/TBW describes how much of that water is outside cells. The two must be read together: more water with a stable ratio is a different pattern from a relative shift towards extracellular water.

If one side is unexpectedly high or changes quickly, check water, ECW/TBW and measurement conditions before calling the difference muscle gain. The result does not establish oedema or another medical condition and does not identify the cause.

Segmental water = amount in litres.
Segmental ECW/TBW = water distribution in that region.
More water can overstate segmental lean mass.
Time of day, recent activity and posture before measurement can especially affect lower-limb results.

Explained values

Water by segmentSegmental body water shows how many litres of water sit in each arm, in the trunk and in each leg separately.ECW Ratio by segmentECW/TBWThe segmental ECW Ratio shows what share of the water in each arm, in the trunk and in each leg sits outside the cells.Lean mass by segmentSegmental Lean Analysis shows how much non-fat tissue — mostly muscle — falls to each of the five body parts: right arm, left arm, trunk, right leg and left leg.ECW RatioECW/TBWThe ECW Ratio states what share of total body water sits outside the cells; it describes distribution, not health status.

Useful comparisons: ECW/TBW ratio vs. total body water →Related guides: Body water, retention and ECW/TBW on InBody →Related guides: Segmental InBody analysis: arms, legs and trunk →Related guides: Why InBody results change after food, training or alcohol →

Phase angle is electrical context, not a segment grade

Segmental phase angle is derived from resistance and reactance in the same body region and is reported at several frequencies.

Phase angle is not another kilogram estimate. It is an electrical quantity in degrees calculated from measured resistance and reactance. A trend comparison must keep the same segment, frequency, device and measurement conditions as consistent as possible.

The manufacturer manual does not provide a universal reference range for segmental phase angle. Do not compare the value with an arbitrary table from another device or population, and do not treat it as a health or “cell quality” score. Its most useful role is a personal repeated trend read alongside water and tissue estimates.

Compare the same frequency and the same body region.
A value in degrees is neither a percentage nor a score.
The manufacturer gives no universal threshold for segmental phase angle.
Interpret trend direction alongside water and lean mass, not in isolation.

Explained values

Phase angle by segmentSegmental phase angle gives the phase angle separately for the right arm, left arm, trunk, right leg and left leg, at three frequencies: 5, 50 and 250 kHz.Phase angleWBPAPhase angle is an electrical quantity in degrees describing the relationship between reactance and resistance measured as current passes through the body — a value for following a trend, not a grade for your health.Water by segmentSegmental body water shows how many litres of water sit in each arm, in the trunk and in each leg separately.Lean mass by segmentSegmental Lean Analysis shows how much non-fat tissue — mostly muscle — falls to each of the five body parts: right arm, left arm, trunk, right leg and left leg.

A side-to-side difference is an observation, not a diagnosis

Asymmetry is more useful when checked across several layers and visits rather than inferred from one deviation.

First verify orientation: right and left on the result are named from the measured person’s perspective. Then check whether the difference appears in one measure only or across lean mass, fat, water and their trends.

A repeated difference can relate to side dominance, an asymmetric sport, previous injury, unequal loading or water status. Bioimpedance cannot identify the cause. If a difference is new, large, accompanied by symptoms or changing quickly, interpretation of possible medical causes belongs with a qualified professional.

Verify the correct side and comparable measurement conditions.
Look for agreement across several layers, not one isolated deviation.
Follow several visits; a small one-off change can reflect measurement variability.
Muscle function cannot be determined from kilograms of lean mass alone.

Explained values

Verified sources for segmental analysis

The meaning of each segmental layer comes from the InBody 970 interpretation manual and manufacturer validation material. Peer-reviewed sources on bioimpedance and phase angle add the limitations needed for single results and cross-device comparisons.

Content reviewed · 2026-07-26

InBody 970 Result Sheet Interpretation (ENG_A_211104)InBody Co., Ltd. · 2021
Validation of InBody 970 (BWA) against DEXAInBody Co., Ltd. · 2021
Bioelectrical impedance analysis – part I: review of principles and methodsClinical Nutrition (ESPEN guidelines) · 2004
Bioelectrical impedance analysis – part II: utilization in clinical practiceClinical Nutrition (ESPEN guidelines) · 2004
Bioelectrical phase angle and impedance vector analysis – clinical relevance and applicabilityClinical Nutrition · 2012
Bioelectrical impedance analysis in body composition measurement: NIH Technology Assessment Conference StatementNational Institutes of Health · 1996

Explanations make the most sense alongside your own trend.

The public guide is open to everyone. The client portal adds your own value, history and the context of a specific measurement.

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