What exactly does Sit-i Pro measure? See how the movement of the seat compares with what you observe in the person and the exercise.
Understanding and using measurement information with Sit-i Pro.
You and a client are looking at a recording together. The seat moved further to the right on the second attempt. ‘That felt smaller,’ the client says. You review the recording again and ask where the movement was felt. The difference on the screen thus becomes the start of a conversation.
A measurement gives you something to refer back to. You can identify a direction, compare two attempts side by side, or review a selected moment again. To make use of it, you need to understand what the displayed value represents. Reviews of motion recording show that accuracy and reliability vary depending on the measured characteristic, system, and task under investigation. [2–5]
Sit-i Pro makes the seat’s movement visible. You connect that recording to what you observe and what the client experiences. This article helps you interpret that information: from the meaning of an angle to the difference between measuring accurately and a value with many decimal places. Flow Analyst, part of the Sit-i Academy, builds on learning how to use that information in your own practice.
What movement is shown on the screen?
When someone moves on Sit-i, you see several things at once. The seat tilts or rotates, the body moves with it, and the client describes how the task feels. Sit-i Pro records the direction and angular change of the seat, including tilting and rotation.
The recording shows, for example, that the seat tilted further to the left. When reviewing it, you also follow the person. What did the feet do? How did the upper body move along? The recording helps you identify a moment you want to discuss further.
The location where you measure also determines what a value refers to. An angle of the seat describes the seat’s position. To measure a separate movement of the spine, you need suitable additional measurement information. Always therefore state which part you are recording.
Targeted measurement of body movement is its own field of research. A systematic review from 2024 found favourable results for measuring movements of the lumbar spine using the body sensors and setups investigated. [2] That application shows how specific measurement research is: the sensor setup and the movement under investigation belong to the conclusion.
During guidance, you can allow the different sources of information to coexist. ‘The seat tilted further’ describes the recording. ‘I felt more movement on the left side’ is the client’s experience. Ask the client which moment that experience refers to and review it together.
The starting position is part of the movement
With Sit-i Pro, the seat’s neutral position, shown as zero degrees, is a reference point. From that position, you can view direction and angular change. This makes it possible to indicate where an attempt begins and where the seat subsequently moves.
Take a hypothetical example. In a first attempt, the seat starts at zero degrees and ends at six degrees. In a second attempt, it starts at two degrees and again ends at six. The final position is the same, while the angular change from the start differs. These fictional values illustrate why the start belongs to your description.
A final value therefore tells you something different from the displacement from the starting point. If you want to know how far someone tilted the seat from a selected position, you look at that change. If you want to describe the position reached, you state the position relative to the reference.
The technical zero position indicates where the system sets its reference. Which starting position is appropriate for an exercise is discussed based on the task. Note in your records how the client started, so you can later review what you compared.
When reviewing, you can indicate the start and then follow the movement. Ask the client whether that starting position was recognisable. The recording thus concerns an execution that you both experienced together.
Make it clear what you are comparing
You want to compare two attempts and see a difference. Then review how they were performed. Perhaps the chair was higher at one point, a foot slipped, or you changed the instruction. That is information that belongs in the comparison.
The COSMIN methodology lists equipment, settings, instructions, and the person performing the measurement as possible sources of differences in outcomes. [1] Measurement therefore also includes the way you prepare a task and have it performed.
Agree beforehand what will remain the same. For example, note the seat height and foot placement, and use the same words when asking a task to be repeated. Follow the corresponding operating instructions before preparing Sit-i Pro. A brief note is sufficient to later find out what you did.
A deliberate change can itself be the focus of the session. You have a client place their feet differently and review the tilting of the seat again. Then you are comparing two foot positions within that task. State which position belonged to which attempt and ask what the client noticed in both executions.
Also state whether you are repeating the measurement during one session or performing it again on a different day. At a subsequent visit, the setup must be prepared again. Your notes make visible which parts you reused and what has changed.
Reliability and accuracy are different questions
A system can give comparable outcomes upon repetition. In addition, you want to know how well those outcomes match a suitable reference measurement. Researchers look at reliability and validity for this, among other things. [2, 3]
Think of a measuring device that has the same fixed deviation in every measurement. The outcomes are close together but still differ from the reference. Therefore, you want to know both whether a measurement is consistently repeated and how large the deviation from the reference is.
In research on reliability, the design matters. Re-evaluating the same recording is different from performing and recording the entire task again. [1] Therefore, when looking at a research result, ask what was actually repeated. That helps you understand for what use the result is relevant.
The chosen measurement outcome also makes a difference. A systematic review and meta-analysis of older adults living independently found good results for various measurements during walking, including walking speed and time per step. For outcomes regarding variation and symmetry, the findings were less unambiguous. [4]
Furthermore, a calculated ratio, such as a symmetry measure, requires an explanation of the calculation. Which values are combined and how was that ratio investigated? That helps to assess a statement about ‘reliable measurement’ for the number you actually use.
Why the research setting matters
A measurement method is always investigated somewhere. The participant performs a task, the system uses a certain setup, and the researchers compare the outcome with a reference. To properly interpret a research result, you take that situation into account.
A meta-analysis from 2025 on body sensors during walking shows this concretely. The deviations from the reference measurements were on average smaller for the ankle and knee movements under investigation than for the hip. When walking on a treadmill, deviations increased. [3] The same type of technology therefore did not yield the same measurement quality under all circumstances.
That is a reason to look beyond the conclusion in a publication. Was it about walking, jumping, or another task? Where were the sensors located, and what movement was measured? Compare that description with the movement and setup about which you want to know something.
For Sit-i Pro, this requires clear delimitation. The studies in this article concern other measurement setups and applications. They help to understand the principles of motion recording; specific statements about the accuracy of Sit-i Pro require research into Sit-i Pro itself.
When reading, you can make a brief summary: this system, this movement, this group of participants, and this comparison with a reference. This allows you to quickly see what was investigated and what questions the publication leaves open.
Many decimal places do not make a difference certain
A small deviation on the screen can make you curious. Perhaps two attempts move almost identically, but you still see a different value. To know what such a difference means, you need information about the measurement error: the deviation that is not attributed to an actual change. [6]
Measurement error is investigated with repeated measurements in a stable situation and can be expressed in the unit of the outcome. [6] The number of decimal places in a display is something different. A device can show a value in detail, while you still do not know what small differences it can accurately distinguish.
If two values are close together, first describe the difference you recorded. Then compare it with the available data on measurement error for that measurement. This allows you to investigate whether the deviation is larger than the uncertainty that belongs to the measurement.
Repetitions during guidance can show what you see in the session. For example, note that the seat tilted further to the right in multiple attempts. For a formal estimate of measurement error, the measurements must be repeated according to a research procedure designed for that purpose. [6] Keep those two types of information separate in your explanation.
If such an error margin is not known, state that when there is a small difference. ‘This value is slightly higher; we do not yet know if the difference is larger than the measurement uncertainty’ gives the client a concrete explanation. A small deviation thus does not receive more weight than you can substantiate.
Also look at the course
In motion measurements, you can describe different characteristics. The largest excursion is one of them. It shows the furthest point reached in a selected direction. This does not yet describe what happened along the way.
Think of an attempt with a short excursion. A maximum value may precisely represent that moment, while the rest of the exercise proceeded differently. If you want to discuss the entire execution, also include the course. Go back to the moment of the excursion: did the client move a foot, for example, or was the exercise interrupted?
An average gives yet another summary. When you use an average, state over what period or attempts it was calculated. One selected attempt and a summary of a series can both be described, but you want to make it clear which of the two you are discussing.
Also pay attention to the unit and the explanation in every display. Is it an angle, a duration, or a calculated ratio? If the meaning is unclear, include the system’s explanation. This prevents a familiar-looking number from taking on a different meaning than the creator of the outcome intended.
These are general examples of interpreting measurement information. Which displays are available varies by system. For your description, choose a characteristic that is actually recorded and that fits what you wanted to look at during the task.
Image and recording complement each other
A video clip can help you review what happened at a striking moment. For example, you see that the client moved their feet or looked at the screen. The recording provides the measurement information from the same part of the execution. When combining both, state which moment you mean.
An image of the body and a measurement of the seat each describe their own part. In the video, for example, you follow the position of the upper body; the recording shows the tilting of the seat. In your explanation, state which information comes from which source.
Different systems that measure body movement are also not automatically interchangeable. A systematic review from 2025 on recording without body markers found comparable results for many measurement values upon repetition. The agreement with systems with markers differed strongly by task, movement plane, and joint. [5]
If you want to compare values from two systems, find out whether they measure the same characteristic and which definitions and references are used. Also check whether research shows how well the systems agree with each other. That is different from knowing that each system measures consistently on its own.
During guidance, you can start with a moment the client recognises. Show the footage, bring up the measurement recording, and ask what they were trying to do at that moment. A brief review can already make clear which part of the exercise you want to review again.
Learning to interpret with Flow Analyst
In Flow Analyst, you learn to observe and record movement systematically. The training within the Sit-i Academy connects what you see to the measurement information from Sit-i Pro. You practice the difference between describing what is happening and explaining why you think it is happening.
A description can, for example, read: ‘In the second attempt, the seat started further to the right; the feet were in the same place.’ This makes it clear what you have established. You then discuss an explanation for the other starting point, including the client’s experience and your observation of the execution.
That way of working fits both applications of Sit-i Pro. Sit-i Athlete · Pro is aimed at sports, training, and motion analysis. Sit-i Care · Pro is aimed at care. The recording of the seat is used alongside the expertise of the professional and the question of the client.
Keep the task and the relevant circumstances with your material. When you later review your own notes, you can follow what you did again. For statements about measurement quality between different days, research under those circumstances is required. [6] The notes help you recognise which comparison you are making.
‘See. Feel. Refine. Improve.’ takes on a practical meaning here. You see how the seat moved and ask what the client felt. With that information, you refine the description of the execution. Then you choose together what you want to review or try again, and follow what that yields.
What can we conclude?
A motion measurement gives information about a selected characteristic of an execution. The reviews describe possibilities for motion recording and show differences in accuracy and reliability between measured characteristics, tasks, and setups. [2–5] It therefore helps to know what a value describes, how it is obtained, and what uncertainty is associated with it.
With Sit-i Pro, you can review the movement of the seat. Flow Analyst helps you connect the recording to what you observe and what the client tells you. This makes a difference on the screen something you can discuss together with focus.
The next time a value catches your attention, you can start with the moment itself. What movement belonged to it? What did you see happening? And what did the client notice? That is where understanding a measurement in your own practice begins.
Explore further
Academy · Flow Analyst — view the learning pathway
Sit-i Insights — Read more about use
Article 9, ‘What do you see that I do not yet see?’, uses images and measurements as a starting point for collegial reflection. Article 13, ‘From motion analysis to treatment choice’, shows how a healthcare professional weighs measurement information within a clinical decision. This article sticks to what the instrument records and how certain a difference is.
Scientific sources
The publications below support the numbered scientific statements. Four sources are systematic reviews, two of which include meta-analysis. The COSMIN publication and corresponding manual support the explanation of measurement concepts and the assessment of research on measurement quality.
[1] Mokkink, L. B., Boers, M., van der Vleuten, C. P. M., Bouter, L. M., Alonso, J., Patrick, D. L., de Vet, H. C. W., & Terwee, C. B. (2020). COSMIN Risk of Bias tool to assess the quality of studies on reliability or measurement error of outcome measurement instruments: A Delphi study. BMC Medical Research Methodology, 20, 293.
https://doi.org/10.1186/s12874-020-01179-5
[2] McClintock, F. A., Callaway, A. J., Clark, C. J., & Williams, J. M. (2024). Validity and reliability of inertial measurement units used to measure motion of the lumbar spine: A systematic review of individuals with and without low back pain. Medical Engineering & Physics, 126, 104146.
https://doi.org/10.1016/j.medengphy.2024.104146
[3] Bissenov, A., Zhubi, E., Engh, M. A., Gresits, O., Tóth, R., & Terebessy, T. (2025). Concurrent validity of wearable IMUs for sagittal plane lower-limb range of motion during walking and estimated ground reaction forces: A systematic review and meta-analysis. Journal of Orthopaedic Surgery and Research, 20, 891.
https://doi.org/10.1186/s13018-025-06322-w
[4] Yin, L., Xu, X., Wang, R., Li, F., Wang, Y., & Wang, L. (2025). Validity and reliability of inertial measurement units on gait, static balance and functional mobility performance among community-dwelling older adults: A systematic review and meta-analysis. EFORT Open Reviews, 10(4), 172–185.
https://doi.org/10.1530/EOR-2024-0088
[5] Yoma, M., Llurda-Almuzara, L., Herrington, L., & Jones, R. (2025). Reliability and validity of lower extremity and trunk kinematics measured with markerless motion capture during sports-related and functional tasks: A systematic review. Journal of Sports Sciences, 43(17), 1703–1730.
https://doi.org/10.1080/02640414.2025.2518359
[6] Mokkink, L. B., Boers, M., van der Vleuten, C., Patrick, D. L., Alonso, J., Bouter, L. M., de Vet, H. C. W., & Terwee, C. B. (2020). COSMIN Risk of Bias tool to assess the quality of studies on reliability and measurement error of outcome measurement instrument: User manual. Version 1.0, December 2020. Methodological manual; no DOI assigned.
https://www.cosmin.nl/wp-content/uploads/user-manual-COSMIN-Risk-of-Bias-tool_v4_dec-2020.pdf
Scientific justification: the reviews concern body sensors and optical motion recording in specific tasks. They support the general explanation of measurement quality, but do not provide product-specific validation, margin of error, or threshold value for Sit-i Pro. [2–5] The tasks, systems, and quality of the underlying studies examined differ. For example, the review on older adults assessed the studies as being of low to moderate quality. [4] The COSMIN sources are methodological sources and are not an effectiveness study or meta-analysis. [1, 6]
The examples with numbers, maximum values, and averages are general illustrations and do not describe product specifications of Sit-i Pro. Practical suggestions for comparison and recording do not constitute a validated measurement protocol. Statements about accuracy, repeatability, and measurement error require data for the system used, the measurement outcome, and the procedure.