Segmental Body Phase Angle
Segmental 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.
Short answer
Fifteen numbers look complicated, but the rule is simple: compare the same segment and the same frequency over time, or the left side with the right at the same frequency. Neither segments nor frequencies are compared with each other. The manufacturer gives no reference range, so this is a value for following a trend — and a difference between sides is an observation, not a diagnosis.
What the value represents
Whole-body phase angle is one number for the whole body. The segmental version divides it into five parts, so it becomes visible how the electrical properties of tissue differ between arms, trunk and legs. The device measures each segment separately — segments are not calculated from a shared value.
Right and left are always given from the point of view of the person being measured, not the observer. Right arm means your right arm, even though the body silhouette or the table appears to place it on your right. Before comparing sides, confirm you are reading the correct row.
Each segment carries three values, because measurement happens at three frequencies: 5, 50 and 250 kHz. Fifteen phase angle values arise in total — three frequencies for each of the five segments.
The three values for one segment are not three attempts at the same thing. A low frequency does not pass well through the cell membrane while a high one does, so each frequency sees the tissue somewhat differently. Values at 5, 50 and 250 kHz are therefore not interchangeable and are not compared with each other.
As with the whole-body value, a fundamental caveat applies: the manufacturer manual gives no reference range for phase angle. There is therefore no manufacturer-defined boundary for segments either by which a value could be classified.
- The phase angle of an individual segment in degrees, measured separately for the right arm, left arm, trunk, right leg and left leg from the point of view of the person being measured.
- Three frequency-specific values for each segment: 5, 50 and 250 kHz.
- According to the manual it expresses the level of structural integrity and function of the cell membrane in that segment.
- It does not represent a grade for the health of a segment, its strength, its function or its amount of muscle.
- It does not represent a diagnosis. A difference between segments or between sides is an observation, not a finding.
How the value is produced
- A measured value. The phase angle of each segment is derived directly from the resistance and reactance measured in that segment, as phase angle = arctan(reactance ÷ resistance).
- Segments are measured separately thanks to eight-point touch electrodes — each handle and the foot platform carries one current and one voltage electrode.
- The phase angle measurement frequencies are 5, 50 and 250 kHz. The device takes 15 phase angle readings in total (three frequencies × five segments).
- For comparison: impedance is measured at eight frequencies from 1 kHz to 3 MHz, in 40 readings altogether (eight frequencies × five segments).
- Reference comparison: none. The manual gives neither a reference range nor evaluation bands for segmental phase angle. The Z- and T-scores on the evaluation sheet relate to the whole-body value at 50 kHz.
How to read the current value
- Sort out the sides first. Right arm and right leg are yours, not the ones on the right of the picture or the table.
- Always compare the same frequency. The right arm value at 50 kHz is compared with the left arm at 50 kHz, not with a value at 5 or 250 kHz.
- Do not compare segments with each other directly. Arms, legs and the trunk differ in length and cross-section, so the trunk inherently has different impedance from a limb; what makes sense is comparing left and right and following development over time.
- Do not look for a band. The manufacturer manual gives no reference range for segmental phase angle, so the value has no manufacturer-defined boundary by which it could be classified.
- A difference between the right and left side is an observation, not a diagnosis. Segmental phase angle does not establish muscular imbalance, injury, oedema or inflammation.
- Segmental phase angle is not a grade for the health of a particular limb and does not convert into its strength or its amount of muscle.
How to read change over time
- The trend is the main usable information here too, because a reference range is absent.
- Always compare the same segment and the same frequency. Mixing frequencies is the most common error in reading this group of values.
- Keep measurement conditions comparable: similar time of day, similar time spent standing beforehand, no training or sauna immediately before, clean and dry hands and feet.
- Read a change in the same direction across all segments as a whole-body shift (typically hydration) rather than a local phenomenon.
- When a single segment moves and the others hold, check the stance and electrode contact during the measurement first — these show up most in the segmental values.
- On the Comparison Result Sheet the manufacturer shows segmental phase angle for the current and previous measurement side by side; that is the intended use of this group of values.
General principles: how to read change between measurements →
What to read it with
- Whole-body phase angle at 50 kHz – the summary the segments form a breakdown of.
- The segmental ECW Ratio – the most useful companion, because the distribution of water between the inside and outside of cells feeds into phase angle directly.
- Segmental body water – shows how much water is in the segment.
- Segmental lean mass – adds how much non-fat tissue is in the segment; phase angle does not establish quantity.
- Impedance and reactance – the quantities phase angle arises from, where the behaviour across frequencies is also visible.
Common misunderstandings
- Sides are read from the point of view of the person being measured. Your right arm appears on the left of the body silhouette.
- The three values for one segment are not three measurements of the same thing. Frequencies of 5, 50 and 250 kHz travel through tissue differently and their values are not compared with each other.
- Segments are not compared with each other directly. The trunk has different geometry and impedance from an arm.
- A difference between sides is not a diagnosis of muscular imbalance, injury, oedema or inflammation.
- Segmental phase angle is not a grade for the health of a limb or an indicator of its strength.
- There is no manufacturer-defined boundary for segmental phase angle. The manual gives no reference range.
What can affect the result short term
- Stance during the measurement — arms straight and not touching the trunk, thighs apart. Stance affects the segmental values most of all.
- The quality of electrode contact: dry hands and feet need wiping, otherwise electrical contact worsens.
- Position before the measurement — the manual recommends standing for at least 5 minutes, because standing lets gravity draw blood into the lower limbs.
- Time of day: according to the manual water shifts towards the lower half of the body during the day, which shows up mainly in the leg values.
- Training shortly beforehand, which changes perfusion precisely in the loaded segments.
- Hydration, food and drink before the measurement.
- Room temperature outside the recommended 20 to 25 °C, showering or sauna before the measurement.
- The menstrual cycle, during which the amount of body water fluctuates.
What to do next
- Confirm the sides before you start comparing left with right.
- Pick one frequency to follow (50 kHz is the logical one for comparison with the whole-body value) and stay with it across measurements.
- For a segment with a striking value, always open the segmental ECW Ratio and segmental lean mass. Phase angle alone gives no context.
- Do not interpret a one-off difference between sides. Confirm it at another measurement under comparable conditions and with the same stance.
- If the difference is accompanied by swelling, pain, restricted movement or loss of strength, that belongs with a doctor or physiotherapist.
What the value does not determine
- The manufacturer gives no reference range, so a single value has nothing to be related to.
- It does not diagnose muscular imbalance, injury, oedema or inflammation; a difference between sides is an observation.
- Values from different frequencies or different segments are not mutually comparable.
- It does not establish the amount of muscle, the strength or the function of a segment.
- It is not comparable between devices from different manufacturers.
- It was not part of the manufacturer validation study against DEXA.
- It is sensitive to stance and to the quality of electrode contact, which show up most in the segmental values.
On terminology
- Right and left are always given from the point of view of the person being measured, not the observer.
- A frequency is always stated with a phase angle. Phase angle of the right arm without a frequency is not an unambiguous figure.
- Phase angle is a quantity, not a score. It has no target value and no ceiling.
- The manufacturer nowhere labels any segmental phase angle value as normal; it publishes no reference range for this quantity.
When to discuss it with a professional
If a difference between segments is accompanied by swelling, pain, restricted movement or loss of strength, discuss it with a doctor or physiotherapist. The measurement describes the electrical properties of tissue but cannot establish a cause and does not replace an examination.
In more depth, with sourcesIn more depth: why three frequencies are measured and what follows for interpretationExpand the detailed explanation
Phase angle arises because the cell membrane behaves electrically like a capacitor: it briefly holds charge and releases it with a delay, creating a phase shift between current and voltage. Formally, phase angle = arctan(reactance ÷ resistance). The frequency of the current fundamentally changes where the current flows, however. Low frequencies do not pass well through the membrane and travel around cells through extracellular fluid; high frequencies pass through and also capture the environment inside cells. A value at 5 kHz therefore describes a different share of tissue from a value at 250 kHz, even though both are called phase angle. That is why they are not compared with each other and why the frequency must be stated with every value.
Segmental measurement has a reason of its own. Body parts differ in length and cross-section: arms and legs are long and narrow and present high resistance to current, while the trunk is short and wide and its impedance is low. Measuring the body as one unit would almost lose the behaviour of the trunk in the overall result. InBody 970 therefore measures five segments separately using eight-point touch electrodes, where each handle and the foot platform carries one current and one voltage electrode. This produces 40 impedance readings (eight frequencies from 1 kHz to 3 MHz × five segments) and 15 phase angle readings (5, 50 and 250 kHz × five segments). For exactly that reason, though, comparing the phase angle of the trunk with the phase angle of an arm makes no sense — they differ in geometry, not necessarily in the state of the tissue.
For segmental phase angle the manual gives the unit (degrees), the frequencies and the meaning (the level of structural integrity and function of the cell membrane in that segment) — and explicitly no reference range. The reference documentation for InBody 970 lists the missing phase angle range among the figures the sources do not contain, so it must not be filled in from other models or from general knowledge. The review by Norman and colleagues adds that phase angle values depend on age, sex and body build, and that their use requires reference values matching both the population and the device — which holds all the more for segmental values at three different frequencies.
The practical consequence is a limited but honest frame of use: following the development of one segment at one frequency in one person under standardised conditions, or comparing the left and right side at the same frequency. The manual is consistent with that in placing segmental phase angle on the Comparison Result Sheet alongside segmental lean mass and the segmental ECW Ratio, and in interpreting the segmental Cole-Cole plot exactly as the whole-body one. A difference between sides remains under all circumstances an observation about the electrical properties of tissue; InBody does not establish muscular imbalance, injury, oedema or inflammation.
Sources
- InBody 970 Result Sheet Interpretation (ENG_A_211104) — InBody Co., Ltd.
- Bioelectrical phase angle and impedance vector analysis – clinical relevance and applicability — Clinical Nutrition
- Bioelectrical impedance analysis – part I: review of principles and methods — Clinical Nutrition (ESPEN guidelines)
On this page
Related values
Related articles
Where to find it
Whole-body phase angle and segmental phase angle among the additional parameters.
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An InBody measurement is not a diagnostic tool. Results do not determine health status and do not replace a medical examination.
FAQ
Frequently asked questions
Answers to what people ask most often about this value.
Why do I have three different phase angles for each body part?
Because measurement happens at three frequencies: 5, 50 and 250 kHz. A low frequency does not pass well through the cell membrane and travels around cells; a high one passes through. Each frequency therefore describes the tissue somewhat differently and the values are not compared with each other — fifteen values arise in total, three for each of the five segments.
Is right leg my right leg, or the one on the right of the table?
Your right leg. InBody always gives sides from the point of view of the person being measured, so on the body silhouette your right side is drawn on the left. Confirm this before comparing sides.
My phase angle is lower in one leg. Is that an injury or oedema?
The measurement cannot establish that. A difference between segments is an observation about the electrical properties of tissue, not a diagnosis — InBody does not establish muscular imbalance, injury, oedema or inflammation. Confirm the difference at another measurement under comparable conditions and with the same stance; if it is accompanied by swelling, pain or restricted movement, that belongs with a doctor.
Can I compare the phase angle of my trunk with that of my arm?
No. The trunk is short and wide and inherently has low impedance, while an arm is long and narrow. The difference between them reflects mainly segment geometry. What makes sense is comparing the same segment over time, or the left and right side at the same frequency.
What segmental phase angle value is fine?
The manufacturer manual gives no reference range for phase angle — neither for the whole body nor for segments. There is therefore no manufacturer-defined boundary by which a value could be classified. What is usable is following your own development in the same segment at the same frequency under comparable conditions.
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.