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 Backpack Load and Spine Muscles Activity (NCT02725645), a na na study. The primary outcome is Muscle Activity as a Measure of Route Mean Square.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02725645 |
| Phase | NA |
| Condition | Child |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 14 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University Fernando Pessoa |
| Results posted | Yes |
2. Clinical Question
Population
The population named in the record is elementary school children, described as healthy school children. The registry lists Child as the condition and records enrollment of 14. Further eligibility criteria, such as age range, health screening details, or how children were recruited, are not reported in the registry record.
Intervention
The study describes different backpack loading conditions, defined as 0, 10, 15 and 20% of body weight. The intervention is classified as other and named “loading conditions.” The record says the children will be presented with different loading conditions, but does not report the order in which these were applied, the duration of exposure, or whether each child completed every condition.
Comparator
The record does not describe a separate control arm. It identifies a single-group model and notes that allocation is NA. The 0% loading condition is one of the conditions named in the study summary, but the registry does not designate it as a separate randomized control group. The timing and method of comparisons between loading conditions are not reported in the registry record.
Primary question
The stated question is whether different backpack loading conditions influence electromyographic activity of the neck and lumbar muscles of elementary school children. Muscle activity is represented by a route mean square measure derived from normalized EMG signals. The record identifies this as a continuous outcome reported as a mean with standard deviation. Numerical outcome results and an analysis comparing the loading conditions are not reported in the registry record, so the direction and precision of any observed differences cannot be assessed.
3. Trial Design
The registry describes a completed, single-group study sponsored by University Fernando Pessoa. The listed enrollment is 14. The study is titled “Backpack Load and Spine Muscles Activity,” and its official title specifies the influence of different backpack loading conditions on neck and lumbar muscles activity of elementary school children. The record lists the study as not applicable for phase and allocation, and states that masking was none.
The brief summary identifies four loading conditions: 0, 10, 15 and 20% of body weight. It says the purpose was to analyze their influence on electromyographic activity in neck and lumbar muscles. The arm description refers to healthy school children being presented with different backpack loading conditions. This is consistent with the single-group model, rather than a registry description of separate treatment and control arms.
The listed start is 2014-06, the primary completion is 2015-07, and the status is completed. The primary outcome timeframe is described as “one year.” The record does not explain how that timeframe relates to the loading-condition measurements, or whether it refers to follow-up, the overall measurement period, or another convention.
Several design details needed to understand the measurement sequence are not reported in the registry record. These include the order of the conditions, whether condition order was randomized or counterbalanced, whether all children underwent all conditions, how long each exposure lasted, and whether there was a rest or washout interval. The record also does not report the measurement setting, the specific muscle sites, or how many EMG recordings were taken per condition. Without those details, the study can be described as a single-group assessment across loading conditions, but not as a more specific crossover or repeated-measures protocol.
No separate randomized comparator is identified. Accordingly, the registry record does not establish a like-for-like control-arm comparison. Any interpretation of differences among loading conditions would depend on how measurements were collected and analyzed, details that are not reported in the registry 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.
Overall Study
| Stage | Healthy School Children |
|---|---|
| STARTED | 14 |
| COMPLETED | 14 |
| NOT COMPLETED | 0 |
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.
| Characteristic | Unit | Healthy School Children |
|---|---|---|
| Participants analysed | 14 | |
| Age, Categorical: <=18 years | Participants | 14 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 |
| Age, Categorical: >=65 years | Participants | 0 |
| Age, Continuous | years | 8.93 (SD 0.73) |
| Sex: Female, Male: Female | Participants | 9 |
| Sex: Female, Male: Male | Participants | 5 |
| Region of Enrollment: Portugal | participants | 14 |
6. Primary Endpoint
The registry lists the primary outcome as Muscle Activity as a Measure of Route Mean Square, measured over one year.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | milivolts |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is titled “Muscle Activity as a Measure of Route Mean Square.” It is a continuous measure with units listed as milivolts and a summary parameter of mean with standard deviation. The study description identifies the source as electromyographic signals from neck and lumbar muscles. Those signals were filtered with a Notch Filter of 50hz, detrended, converted into millivolts, normalized, and then used to calculate the route mean square. The record identifies MATLAB 7.11 (v.2010) as the software used for the initial filtering step.
In general, an EMG signal records electrical activity associated with muscle activation. A mean-square-type summary can condense a changing signal into a measure of its typical magnitude over a specified recording interval. Normalization is generally used to express signals on a common scale, but the reference method used for normalization is not reported in the registry record. The exact calculation interval and any aggregation across recordings are also not reported in the registry record.
The endpoint is relevant to the stated question because it provides a quantitative measure of muscle electrical activity under the different backpack loading conditions. It is a physiological measurement, not a direct measure of pain, injury, function, or long-term health. The registry record contains no numerical endpoint values, so it does not show the measured activity for any condition or the uncertainty around a comparison.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record defines a research question about backpack loading and neck and lumbar muscle activity, but it does not report the numerical primary outcome results. Although the outcome is identified as a continuous mean with standard deviation, there are no condition-specific means or standard deviations in the available record. There is also no reported estimate of a difference between conditions, confidence interval, p-value, or other inferential statistic. Consequently, the posted information cannot establish the direction, size, or precision of any difference in muscle activity.
The design is listed as single-group, with allocation recorded as NA and masking as none. The summary describes four loading conditions—0, 10, 15 and 20% of body weight—rather than separate randomized groups. The record therefore does not support treating the study as a randomized comparison between independent arms. It also does not explain whether each child experienced every condition or whether condition order was controlled. Those details matter because measurements taken from the same child may be related, and order or measurement conditions could affect observed values.
The enrollment is listed as 14, but enrollment alone does not show how many measurements were available for each condition or whether all enrolled children contributed to the primary endpoint. The analysis population, missing observations, and reasons for any unavailable measurements are not reported in the registry record. Without those details, it is not possible to assess how representative an analyzed set of measurements would be of the enrolled group.
General statistical interpretation of a continuous outcome would consider both the estimated differences and their uncertainty. A confidence interval describes a range of values compatible with the data and the analysis assumptions; it helps distinguish a precise estimate from one with substantial uncertainty. Since the registry record does not report an estimate or interval, precision cannot be assessed. A p-value alone, even if it had been reported, would not describe the size or practical importance of a difference; no p-value is reported in the registry record in any case.
The sample-size assumptions describe a planning illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The illustration is not the study's own design rationale, and the record does not provide its resulting sample-size figures. Its two-arm assumptions do not correspond directly to the listed single-group design and loading conditions. It must not be interpreted as evidence that the study had a particular probability of detecting an effect.
The posted record supports describing what was intended to be measured and how the EMG signal was processed at a high level. It does not provide the outcome data or analysis needed to draw a statistical conclusion about the relationship between loading condition and muscle activity.
9. Statistical Methods Explained
The primary outcome is a continuous measurement summarized as a mean and standard deviation. In general, a mean describes the average observed value in a set of measurements, while the standard deviation describes how dispersed individual values are around that average. A mean and standard deviation do not by themselves show how precisely a comparison between conditions has been estimated. Precision depends on the amount and structure of the data and on the statistical analysis. Condition-level values and a comparative analysis are not reported in the registry record.
What does the EMG processing description tell the reader?
The record says that EMG signals were initially filtered with a Notch Filter of 50hz due to the DC power line, using MATLAB 7.11 (v.2010). It then states that the signal was detrended, converted into millivolts and normalized, and that the normalized signal was used to calculate the route mean square. In general, filtering is a signal-processing step intended to remove a targeted component of a recording, and detrending removes a modeled trend from a signal. Normalization transforms measurements according to a reference or scaling rule. The record does not state the normalization reference, filter settings beyond the stated frequency, or the precise algorithm used to calculate the endpoint.
These omissions affect reproducibility and interpretation. For example, normalized EMG values are meaningful in relation to the normalization procedure, and the route mean square depends on the signal interval and calculation details. The registry record does not report those details, the recording equipment, electrode placement, or quality-control procedures. No assumptions about them can be made from the stated endpoint description alone.
Why does the single-group structure matter?
In general, a single-group study can compare measurements collected under multiple conditions, but the appropriate comparison depends on how observations are related. If the same participants contribute measurements under each condition, the observations are paired or repeated within participant, and analysis should account for that dependence. Treating related measurements as independent can misrepresent uncertainty. If different participants contribute to different conditions, an independent-group approach may instead be relevant. The registry record does not report which data structure applies, so it is not possible to identify the appropriate analysis from the record.
Condition order can also matter in general. Fatigue, adaptation, learning, or changes in measurement setup could influence later measurements. Randomizing or balancing order can help address such effects, but the registry record does not report whether an order procedure was used. This is not evidence that such procedures were absent; it means their use is not reported in the registry record.
What can be inferred from the planning assumptions?
The planning assumptions describe a sample-size illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. In general, such calculations explore how a hypothetical future study might be sized under specified assumptions. They are not observed outcomes and are not a measure of the probability that the completed study detected an effect. The record does not provide the resulting participant counts for the planning scenarios, and the equal-allocation, two-arm assumptions do not describe the listed single-group design.
The record does not report a formal statistical analysis plan or a model for comparing conditions. It lists zero analyses. Therefore, the reader cannot determine whether the intended analysis used a paired method, a repeated-measures model, a regression approach, or another method. Details such as adjustment for baseline measurements, covariates, participant-level clustering, or distributional assumptions are not reported in the registry record.
How should uncertainty and over-dispersion be considered?
In general, a confidence interval communicates uncertainty around an estimated quantity, while a test statistic and p-value address compatibility with a null hypothesis under a specified model. Both require an analysis and data. Neither is reported for the primary outcome. The continuous outcome's mean and standard deviation would describe the values, but without the actual values and analysis structure they cannot establish a condition effect.
Over-dispersion generally refers to variability greater than a statistical model expects. It is particularly relevant to models for counts or binary outcomes; the listed primary outcome is continuous, so the registry record does not identify a count model or an over-dispersion assessment. More broadly, model assumptions should fit the outcome and dependence structure. Since no analysis is recorded, the model assumptions and any diagnostics are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists one primary outcome measure and zero analyses. It does not report a statistical analysis plan, a family of hypotheses, a hierarchy of endpoints, or a method for controlling multiplicity. The four loading conditions create potential for more than one condition comparison, but the registry record does not specify which comparisons were planned or whether any adjustment for multiple comparisons was intended. It is therefore not possible to assess how multiplicity was addressed.
In general, testing multiple hypotheses can increase the chance of finding at least one apparently unusual result when no real differences exist. A prespecified comparison strategy or multiplicity adjustment can help interpret a set of tests. That general concern does not establish that the study conducted multiple tests; the number and type of inferential analyses are not reported in the registry record.
Missing-data handling is not reported in the registry record. The record does not describe whether any endpoint measurements were missing, why they might have been missing, or how missing observations would be handled. It also does not identify an analysis population, such as all enrolled children or a defined subset with usable EMG recordings. The enrollment of 14 should not be taken as proof that complete primary outcome data were available for every loading condition.
In general, missingness can affect interpretation if the availability of measurements is related to participant characteristics or observed outcomes. A complete-case analysis, imputation method, or sensitivity analysis would each involve assumptions that should be described. No such approach is reported. The record also does not state how repeated measurements, if any, were handled or whether all measured muscles and conditions were included in a common analysis.
Because results and analyses are not reported, there is no basis to evaluate selective reporting or to compare analyses with a prespecified plan. The registry record does not report such a plan.
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 |
|---|---|---|---|
| Healthy School Children | 0 | 14 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Healthy School Children | 0 of 14 |
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 |
|---|---|
| Healthy School Children | 0 of 14 |
The adverse-event record lists Healthy School Children as the group. It records 14 at risk for serious adverse events and zero with serious adverse events. For other adverse events, it also records 14 at risk and zero affected. The death count is zero. No serious adverse event terms are listed.
These entries describe what is recorded in the registry's safety fields. They do not, on their own, show how adverse events were defined, how they were collected, how long participants were monitored, or whether an event was judged related to a loading condition. Those details are not reported in the registry record. The primary outcome timeframe is listed as “one year,” but the safety follow-up period is not separately described.
Zero recorded events should be read as zero events entered in the reported fields, not as proof that an exposure is risk-free. The record does not provide enough information to assess the sensitivity of event collection or to characterize possible minor or transient effects. The at-risk figures are reported for the safety categories; they should not be interpreted as evidence about how many condition-specific observations were made.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a completed single-group study was intended to examine muscle activity under different backpack loading conditions in elementary school children. Its primary endpoint was a continuous EMG-derived measure described as route mean square, reported in milivolts and summarized by a mean with standard deviation. The stated conditions were 0, 10, 15 and 20% of body weight.
The record does not report numerical outcome results, condition-specific summaries, comparisons, confidence intervals, or p-values. As a result, it does not show whether the measured muscle activity varied among the conditions, the direction of any variation, or how precisely an effect was estimated. No conclusion about a difference can be drawn from the endpoint description or study objective alone.
Even if condition-specific activity values were available, an EMG measure would represent muscle electrical activity under the measurement protocol. In general, it would not by itself establish pain, injury, functional impairment, or long-term consequences. The record does not report clinical outcomes of that kind. It also does not provide details about the loading sequence, participant-level measurement structure, or analysis, all of which would inform interpretation of comparisons.
The safety fields report zero serious adverse events, zero other adverse events, and zero deaths. These are registry entries, not a complete account of event definitions or monitoring. The record does not report event-collection procedures or a separate safety follow-up description.
The planning assumptions are illustrative rather than a description of the study's design justification or a measure of observed power. They assume equal allocation between two arms and a normal approximation, while the registry lists a single-group study. The record does not report its sample-size rationale. Overall, the registry provides a description of the study question and measurement process, but not the outcome evidence needed to assess the observed relationship between backpack loading and muscle activity.
13. Why This Trial Matters Statistically
This study raises a statistical question that is common in physiological research: how to compare a continuous signal measured under more than one condition. The key issue is not only the number of conditions, but also how measurements are linked to participants. If the same child contributes data under multiple conditions, those values are statistically dependent. An analysis that accounts for that structure can differ from one that treats all observations as independent. The registry record does not state the measurement structure or analysis, making this a central interpretive gap.
The endpoint also depends on signal processing. Filtering, detrending, conversion to millivolts, normalization, and calculation of a route mean square each contribute to the definition of the outcome. Clear reporting of the normalization reference, recording procedure, and calculation interval would help readers reproduce the measure and understand what a difference represents. Some processing steps are described, but these additional details are not reported in the registry record.
Another statistical lesson is the separation between a study objective and its results. The record states a question and names an outcome but supplies no numerical findings or analysis. A stated aim does not establish that an effect was observed. Similarly, enrollment alone does not establish the precision of a comparison, and a planning illustration is not evidence of observed power.
The record is useful as an example of why transparent reporting includes more than an endpoint label. Readers need outcome values, a clearly defined comparison, an analysis suited to the data structure, and a description of uncertainty. Without those elements, even a clearly stated research question cannot be translated into a quantitative conclusion.
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 direct limitation of the available record is that it contains no numerical primary outcome results or statistical analyses. It lists one outcome measure and zero analyses, so there is no reported estimate of the relationship between loading condition and muscle activity. The record also does not report condition-specific means or standard deviations, uncertainty intervals, or hypothesis tests.
The design description is limited. Although it identifies a single-group model and four loading conditions, it does not state whether every child underwent every condition, how condition order was determined, or how long each measurement lasted. It also does not describe the number of observations per child or the exact muscles and EMG recording sites. These gaps prevent assessment of the appropriate comparison structure and possible order or measurement effects.
Participant eligibility and recruitment details are not reported in the registry record beyond the description of healthy elementary school children. The record does not provide age ranges, setting details, or information about representativeness. Enrollment is listed as 14, but the number contributing usable data to each condition is not reported. Missing-data procedures and analysis populations are also not reported.
The endpoint processing description does not identify the normalization reference, precise route mean square calculation, recording interval, or detailed signal-quality procedures. Such details are relevant to reproducibility and to interpretation of values across conditions. The statistical analysis plan and rationale for the sample size are not reported. The planning illustration uses two-arm assumptions that do not directly match the listed single-group design.
Finally, adverse-event entries do not include definitions, collection methods, attribution, or a distinct safety follow-up period. The reported zero counts should therefore be interpreted within the limits of the registry fields rather than as comprehensive evidence about safety.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Backpack Load and Spine Muscles Activity — NCT02725645.
- Registry record last updated 2019-10-28; status last verified 2019-10.
- Results first posted 2019-10-28.
- 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
NCT02725645 is a completed, single-group study sponsored by University Fernando Pessoa. It lists enrollment of 14 and describes healthy elementary school children exposed to backpack loading conditions of 0, 10, 15 and 20% of body weight. Allocation is NA and masking is none. The listed start is 2014-06 and primary completion is 2015-07.
The primary outcome is a continuous EMG-derived measure titled “Muscle Activity as a Measure of Route Mean Square,” with units of milivolts and a mean with standard deviation. The description includes filtering, detrending, conversion, normalization, and route mean square calculation. Numerical results and statistical analyses are not reported in the registry record.
The safety entries list zero serious adverse events, zero other adverse events, and zero deaths. Further details on event collection, missing data, analysis populations, and the statistical plan are not reported in the registry record.