This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Chairless Chair Exoskeleton. Work-physiological-biomechanical Analysis of the Lower Extremities (NCT03134144), a randomized na study. The primary outcome is Center of Pressure.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03134144 |
| Phase | NA |
| Condition | Healthy |
| Allocation | Randomized |
| Design model | Crossover |
| Masking | None (open label) |
| Enrollment | 46 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University Hospital Tuebingen |
| Results posted | Yes |
2. Clinical Question
Population
Healthy participants were enrolled to perform assembly tasks in a laboratory setting. The registry record reports enrollment of 46 participants and notes that two dropped out because information about the base of support was missing; that information was needed to calculate center of pressure. The proposed inclusion of people with different body heights was intended to examine whether height influenced the device’s effects. The record does not report the body-height distribution or results by height.
Intervention
The intervention was the lower-leg exoskeleton called the Chairless Chair. It allows a person to adopt a technically seated position while carrying out standing work. The registry describes evaluating the device during assembly tasks, with physiological and biomechanical measures. It does not report numerical outcome results for the device condition.
Comparator
The comparator was performing the conditions without the exoskeleton. Participants were assigned to one of two orders: without the device followed by with it, or with the device followed by without it. This is a crossover arrangement, rather than a comparison of separate parallel groups. The registry record does not report how much time elapsed between conditions.
Primary question
The primary endpoint was the anteroposterior center of pressure, measured in millimeters. The study asked whether this balance-related measure differed when participants performed the tasks with versus without the exoskeleton. The record describes the measure and its sign convention, but numerical results for the comparison are not reported in the registry record.
3. Trial Design
This was a randomized, unmasked crossover study. Its registry enrollment was 46, and its status is completed. The record lists the study as phase not applicable and identifies healthy participants. The sponsor was University Hospital Tuebingen. The study began on 2017-05-01, and primary completion was recorded as 2017-10-15.
In a crossover design, participants experience both conditions, so each person can serve as their own comparator. Here, the two conditions were performing tasks with and without the Chairless Chair. Randomization assigned the order: one sequence performed tasks without the exoskeleton first and with it second; the other sequence reversed that order. The registry identifies allocation as randomized and masking as none. It does not report how the random sequence was generated or whether allocation was concealed.
The study was designed for laboratory evaluation of assembly tasks, comparing device use with non-use on physiological and biomechanical parameters. The registry summary describes an interest in whether body height influences the device’s effects because the exoskeleton is made in one size. It does not report the specific tasks in enough detail to characterize their duration, workload, or sequence beyond the stated measurement timeframe.
There is no reported washout interval, and the registry record does not describe procedures for managing possible order, practice, fatigue, or carryover effects. It also does not report a statistical analysis plan, sample-size justification, interim analyses, or numerical primary-outcome results. The study’s completed status indicates its registry status, not that all planned outcomes or analyses are available in the record.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Before assignment: None of the recruited volunteering participants was excluded based on the exclusion criteria. One subject dropped out prior to the measurement due to time constraints.
Overall Study
| Stage | First Without Exoskeleton Then With Exoskeleton | First With Exoskeleton and Then Without Exoskeleton |
|---|---|---|
| STARTED | 15 | 30 |
| COMPLETED | 15 | 30 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: In total, two participants dropped out due to missing information with regard to the base of support, which is necessary to calculate the centre of pressure.
5. Baseline Characteristics
The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.
Population: Three additional subjects were recruited on top of the the sample size calculation, because three of the earlier measured subject had some missing data due to technical problems.
| Characteristic | Unit | First Without Exoskeleton Then With Exoskeleton | First With Exoskeleton Then Without | Total |
|---|---|---|---|---|
| Participants analysed | 15 | 30 | 45 | |
| Age, Continuous | years | 23.9 (SD 2.7) | 25.2 (SD 3.0) | 24.8 (SD 2.9) |
| Sex: Female, Male: Female | Participants | 0 | 0 | 0 |
| Sex: Female, Male: Male | Participants | 15 | 30 | 45 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Center of Pressure, measured over 10 minutes of 2 hours.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Inter-Quartile Range |
| Unit | mm |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint was center of pressure, recorded in millimeters using a force plate. The registry describes center of pressure as a visual projection of a participant’s center of mass and as an indicator of balance. The recorded primary measure was the anteroposterior direction, rather than the mediolateral direction. A positive value represents movement toward the anterior direction, and a negative value represents movement toward the posterior direction.
Balance-related measurements can help characterize how a person maintains posture while completing a task. In this study, that measure was intended to capture a biomechanical feature that might change when the exoskeleton is worn. The timeframe was 10 minutes of 2 hours. The registry identifies the median as the summary measure and the inter-quartile range as the dispersion measure.
These descriptions clarify what the endpoint represents, but they do not indicate the direction or size of any observed difference between conditions. Numerical endpoint results and a comparison estimate are not reported in the registry record. The record notes that two participants dropped out because base-of-support information needed for calculating center of pressure was missing; it does not provide further detail about missingness or the analysis population.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes the study question and endpoint but does not report numerical results for the primary comparison. Consequently, the center-of-pressure values for the device and non-device conditions, the estimated difference between conditions, and any uncertainty measure are not reported in the registry record. No conclusion about the direction, magnitude, or precision of a primary-outcome difference can be drawn from the record.
The endpoint was defined as anteroposterior center of pressure in millimeters, with positive values denoting the anterior direction and negative values the posterior direction. This sign convention would be important when interpreting any numerical comparison: a shift in either direction is not automatically beneficial or harmful. The registry identifies the median and inter-quartile range as the descriptive summary and dispersion, respectively, but supplies no values to interpret.
The crossover design gives each participant experience in both conditions, which can support within-person comparisons. In general, this can reduce the influence of stable differences between participants. However, interpretation also depends on whether condition order, learning, fatigue, or effects that persist from one condition into the next are addressed. The registry records randomized order but does not report an analysis accounting for period or carryover effects, or whether a washout interval was used.
The record notes a loss of primary-outcome information for two participants because base-of-support information required for calculating center of pressure was missing. It does not report whether missingness differed by condition, how the missing values were handled, or the number included in the primary analysis. The enrollment figure should not be treated as the analysis denominator.
The registry lists no analysis entries and does not give a primary-outcome estimate, confidence interval, or p-value. It also does not report whether the comparison was adjusted for any covariates or whether results were assessed by body height. The study’s completed status and its design description do not substitute for outcome results. Accordingly, the record supports describing the intended comparison and measurement, but not asserting that the device changed center of pressure or that any change was precise, statistically significant, or practically important.
9. Statistical Methods Explained
What does a crossover design compare?
In a crossover study, the same participants receive or experience each study condition, in a specified order. The main comparison can therefore be based on the difference within each participant, rather than comparing only separate groups of people. This design can account for stable participant characteristics because those characteristics are shared across the conditions experienced by the same person. It does not remove every source of bias or variability: order, learning, fatigue, and effects that persist between conditions can influence measurements.
For this trial, the registry describes randomized assignment to one of two sequences, with participants performing tasks first without and then with the exoskeleton, or first with and then without it. Randomizing order can help prevent systematic assignment of a particular condition to a particular period. The record does not specify the randomization procedure, report a washout interval, or describe an analysis for period or carryover effects. Those details are relevant when assessing how well the observed within-person comparison isolates the condition difference.
What does randomization establish?
Randomization is a method for assigning the sequence by chance, rather than by a participant or investigator choosing the order. It can reduce systematic differences in assignment, but it does not guarantee balance in every feature of a small study, and it does not ensure that the analysis is free from bias. Here, the registry states that allocation was randomized. It does not describe sequence generation or concealment. Masking was listed as none, so participants and study staff were not described as masked to the condition. The record does not say whether outcome processing was masked.
How should the endpoint summaries be read?
The primary endpoint was anteroposterior center of pressure, measured in millimeters. The registry identifies the median as the summary and the inter-quartile range as the dispersion. In general, the median describes the central point of a distribution when observations are ordered. The inter-quartile range describes the spread of the middle portion of the distribution. These summaries can be useful when data are skewed or contain values far from the center, because they are less influenced by extreme observations than the mean and standard deviation.
A confidence interval, in general, expresses uncertainty around an estimated quantity under the assumptions of the analysis. It can help readers judge which effect sizes are compatible with the data, rather than relying only on whether a test crosses a significance threshold. No confidence interval or numerical estimate for the primary comparison is reported in the registry record, so its precision cannot be assessed.
Why can over-dispersion matter?
In general, over-dispersion means the observed variability is greater than a statistical model expects. If a model assumes less variability than the data contain, its uncertainty estimates can be too small and statistical tests can be misleading. The registry record does not describe a count outcome or a model for which over-dispersion is identified as an issue in this trial. It also does not report the statistical model used for the primary endpoint. Over-dispersion should therefore be understood as a general consideration, not as a reported feature of these data.
What statistical plan is available?
The registry lists no analysis entries. A statistical analysis plan, a description of covariate adjustment, and a justification for the planned enrollment are not reported in the registry record. The record also does not report interim analyses. Without these details and without outcome estimates, it is not possible to determine how the planned analysis was implemented or whether it matched a prespecified plan.
The registry describes the primary endpoint as a median with inter-quartile range, but that does not by itself identify the method used to compare conditions. A comparison might be expressed as a within-participant difference or use a model that accounts for repeated measurements; which approach was used is not reported. Nor does the record report how the analysis addressed the randomized sequence, period effects, missing measurements, or the stated interest in body height.
Planning calculations based on an observed effect, when used, are illustrations for future study planning and are not observed power for the completed trial. The registry record does not provide numerical planning illustrations for interpreting the primary comparison. No outcome estimate can be reconstructed from the endpoint definition alone.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists the primary center-of-pressure outcome and additional outcome measures, including upper-back forward flexion, subjective overall discomfort, and participant evaluation. Considering multiple outcomes or multiple categories and time points can raise multiplicity concerns: the more comparisons examined, the greater the chance that some appear notable by chance alone. Whether and how multiplicity was addressed is not reported in the registry record.
The record indicates that the primary outcome has several categories or time points and was not reduced to one comparison in the posted analysis information. It does not identify a single numerical primary contrast, provide results for those categories or time points, or describe a hierarchy for interpreting outcomes. No adjustment method or prespecified strategy for prioritizing comparisons is reported.
For the primary endpoint, the registry notes that two participants dropped out because required base-of-support information was missing. It does not report whether data were missing for other reasons, whether the missingness differed between conditions, or how missing values were handled. The record also does not state the number analyzed for the primary endpoint. Missing data can affect precision and can bias a comparison when the reasons for missingness are related to the measurement or condition; the available record does not allow that possibility to be evaluated.
The registry provides no analysis entries and does not define analysis populations, such as all randomized participants or participants with measurements in both conditions. It is therefore unclear which population was used for any primary or secondary analysis. The enrollment figure, outcome-specific dropout note, and adverse-event denominators describe different record elements and should not be treated as interchangeable analysis counts.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Without Exoskeleton | 0 | 45 | 0.0% |
| With Exoskeleton | 0 | 45 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Without Exoskeleton | 0 of 45 |
| With Exoskeleton | 0 of 45 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Without Exoskeleton | 0 of 45 |
| With Exoskeleton | 0 of 45 |
The registry lists safety figures separately for the without-exoskeleton and with-exoskeleton conditions. It reports 45 participants at risk in each condition. In both, the recorded count for serious adverse events was 0, the count for other adverse events was 0, and deaths were 0. No serious adverse-event terms are listed.
These figures describe what was entered in the registry’s safety record. They do not establish that no discomfort or other event occurred outside the recorded categories, and they do not indicate how events were actively monitored or defined. The record does not provide event narratives, severity details, or an explanation of the safety denominators. Because the study is a crossover, the two condition-specific at-risk figures should not be interpreted as separate parallel groups or added to infer a number of distinct participants.
Zero recorded events is not proof that an event is impossible or that the device has no safety risks. The figures should be read narrowly as the posted adverse-event counts for the listed categories and conditions. They do not provide evidence about longer-term safety beyond the registry’s reported information.
12. What the Result Does, and Does Not, Mean
This study addresses a relevant measurement question: whether a balance-related biomechanical measure changes when healthy participants perform laboratory assembly tasks wearing the Chairless Chair rather than without it. The registry identifies the anteroposterior center of pressure as the primary endpoint and describes a randomized crossover design. It also records the rationale for studying body height, given that the exoskeleton is made in one size.
The record does not report numerical primary-outcome results. It therefore cannot establish whether center of pressure differed between conditions, which direction any difference took, or how large or precise it was. The stated use of the median and inter-quartile range describes the planned form of summary but supplies no observed values. A significance result, confidence interval, or estimate of clinical importance is not available in the registry record.
The study question is also narrower than whether the device reduces musculoskeletal symptoms or improves workplace health. The primary measure is an objective balance-related parameter recorded during a specified laboratory measurement period. The listed secondary outcomes include posture, perceived discomfort, and participant evaluation, but their numerical results are not reported in the registry record. The available information does not demonstrate effects on injury, long-term discomfort, work productivity, or other outcomes beyond those described.
Even if a numerical difference were available, its interpretation would depend on measurement variability, the analysis of repeated conditions, possible period or carryover effects, missing data, and the practical relevance of the difference. Those details are not reported. The appropriate conclusion from this record is that it documents the study design, endpoint definition, and safety counts, while leaving the primary comparative result unavailable.
13. Why This Trial Matters Statistically
The study is statistically interesting because a crossover design fits a question in which participants can be assessed both with and without a wearable device. Within-participant comparisons can reduce the influence of stable differences between people, which is useful when biomechanical measurements vary across individuals. Randomizing the order of conditions is also relevant because task performance can change with practice or fatigue.
At the same time, crossover comparisons require careful attention to the sequence and timing of measurements. If a participant’s experience in one condition affects performance in the next, a simple contrast may combine device effects with period or carryover effects. The registry record describes randomized sequence assignment but does not report a washout interval or statistical handling of these effects. This makes the unavailable analysis details important for interpreting any future or separately reported estimates.
The endpoint also illustrates why clear measurement definitions matter. The registry specifies the anteroposterior direction, millimeter units, sign convention, instrument, summary measure, and measurement timeframe. Those details provide a framework for interpreting a result if one is reported, while the absence of numerical results prevents judging its size or precision. The record’s note about missing base-of-support information further highlights that data availability can depend on the requirements of a derived biomechanical measure.
Finally, the study distinguishes a laboratory outcome from broader occupational claims. A balance-related endpoint during assembly tasks is not equivalent to evidence about long-term health or workplace effectiveness. The statistical value of the study depends on both the design and transparent reporting of the comparison, its uncertainty, and its missing-data handling. Those outcome and analysis details are not reported in the registry record.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The most consequential limitation for interpreting this record is that numerical results for the primary endpoint are not reported in the registry record. Without condition-specific summaries or a comparison estimate, the observed effect and its precision cannot be assessed. The record lists no analysis entries, so the method used to compare conditions is also unavailable.
The registry notes that two participants dropped out because base-of-support information needed to calculate center of pressure was missing. It does not explain when or why that information was unavailable, whether missingness was related to condition, or how the resulting data were handled. The analysis population and the number with usable primary-outcome measurements are not reported. Enrollment should therefore not be mistaken for the denominator in an endpoint analysis.
The unmasked design may permit expectations or awareness of condition to influence subjective ratings or study conduct. The registry does not report whether outcome processing was masked. Since participants experienced conditions in sequence, possible practice, fatigue, period, and carryover effects are also relevant; the record does not describe a washout interval or an analysis addressing these factors.
The study summary refers to laboratory assembly tasks and a proposed assessment of body-height influence, but outcome results by task or body height are not reported. The record does not provide enough information to evaluate how well laboratory performance represents actual workplace conditions. The registry lists healthy participants, so the record does not establish results for other populations. These limitations concern what can be concluded from the available registry information, not proof that the study procedures or analyses were inadequate.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Chairless Chair Exoskeleton. Work-physiological-biomechanical Analysis of the Lower Extremities — NCT03134144.
- Registry record last updated 2020-06-16; status last verified 2020-06.
- Results first posted 2020-06-16.
- Data retrieved from ClinicalTrials.gov on 2026-11-09.
- Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.
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18. Record Summary
NCT03134144 is a completed randomized, unmasked crossover study sponsored by University Hospital Tuebingen. The registry records enrollment of 46 and describes healthy participants performing tasks with and without the Chairless Chair exoskeleton, in randomized condition order. The study began on 2017-05-01, with primary completion on 2017-10-15.
The primary endpoint was anteroposterior center of pressure in millimeters, summarized by the median and inter-quartile range over 10 minutes of 2 hours. Positive values indicate the anterior direction and negative values the posterior direction. The record notes two dropouts because information needed to calculate center of pressure was missing. It lists zero serious adverse events, zero other adverse events, and zero deaths in each condition-specific safety record.
Numerical primary-outcome results, the analysis method, the analysis population, and a statistical analysis plan are not reported in the registry record. The record therefore describes the question and measurement but does not establish the direction, magnitude, or precision of a difference between conditions.