Feasibility of HIIT in Spinal Cord Injury: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Feasibility of HIIT in Spinal Cord Injury (NCT03152110), a na na study. The primary outcome is HIIT Times.

2. Clinical Question

3. Trial Design

This completed study is registered as “Feasibility of HIIT in Spinal Cord Injury,” with the official title “Feasibility and Acceptability of Six-weeks of High Intensity Interval Training in Wheelchair Users With SCI.” The sponsor is the University of Pittsburgh. The registry lists the study as a single-group intervention, with no masking and no randomized allocation. Its phase is listed as not applicable.

The planned enrollment was 10. The study population was described as untrained individuals with spinal cord injury or disease who use a manual wheelchair full time. The registry summary describes screening and a requirement for medical release from a participant’s physician before testing. It also describes the rationale for investigating an upper-extremity exercise program: conventional lower-limb interval exercise may not be suitable for this population, and research on high-intensity interval training in people with spinal cord injury was described as limited.

The intervention was named HIIT. Sessions were planned 3 times per week for 6 weeks, with 2 supervised sessions and 1 unsupervised session each week. The training goal was 10 sets of 60-second arm-cycling bouts at 90% of peak power output, with 60 seconds of active recovery. These are descriptions of the planned exercise program; the registry record does not report how consistently participants completed each element.

The primary outcome was the number of work and rest intervals completed per session, averaged over sessions and participants. The primary analysis population was participants who completed at least one HIIT session, stated as 9 participants. The record lists perceived exertion, adapted perceived exertion, and feelings during HIIT among secondary outcomes. It also lists 10 outcome measures overall. The registry dates are a study start of 2018-01-02 and primary completion of 2019-08-31, and the overall status is completed.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis performed only on the numbers of participants who completed at least one HIIT training session (n=9)

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.

6. Primary Endpoint

The registry lists the primary outcome as HIIT Times, measured over To be recorded weekly, throughout study completion (3x/week for 6 weeks).

The primary endpoint, “HIIT Times,” measures the number of work and rest intervals completed by participants during a training session. The registry defines the reported measure as an average across all sessions and participants. Its unit is intervals, and the intended summary is a mean with a standard deviation. The timeframe is described as weekly recording throughout study completion, with sessions scheduled 3 times per week for 6 weeks.

This endpoint is relevant to a feasibility study because it describes whether participants completed the interval structure of the exercise sessions. Counting completed intervals is a direct way to characterize participation in the prescribed work-and-recovery format. It does not, by itself, establish why a participant completed fewer intervals, whether the training was acceptable, or whether fitness changed. Those questions would require other recorded measures and results.

The registry states that the primary analysis was performed only among participants who completed at least one HIIT training session, and gives that analysis population as 9. The actual mean number of intervals and standard deviation are not reported in the registry record. Consequently, the endpoint’s definition and analysis population can be described, but its observed level and variability cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The study’s design determines what its results can describe. This was a single-group study with no randomized allocation and no masking. Participants undertook a HIIT program, and the primary endpoint counted completed intervals. Since the record does not include a separate control group, the primary endpoint is descriptive: it can summarize interval completion in the study group, but it cannot estimate a difference between HIIT and a comparator.

What does a mean describe?

General statistical explanation: a mean is a measure of the center of a set of observations. For this endpoint, the registry specifies a mean number of intervals, averaged across sessions and participants. A mean can provide a compact description of typical completion, but it does not show whether individual participants had similar results or whether session completion varied over time. The record specifies a standard deviation as the accompanying measure of spread. General statistical explanation: a standard deviation describes dispersion around the mean; a larger value indicates more spread in the observations, while a smaller value indicates that observations are more concentrated. Neither numerical summary is reported for this endpoint in the registry record.

What would a confidence interval add?

General statistical explanation: a confidence interval expresses the uncertainty around an estimated quantity under the statistical method used. It gives a range of values compatible with the data and method, rather than a guarantee that the true value lies within that range. The registry record does not report a confidence interval for the primary outcome, nor does it report an inferential estimate for a treatment contrast. Because the study is single-group, a confidence interval around the mean completion measure would address uncertainty about that group’s average, not a comparative effect against a control.

How should the analysis population be understood?

The primary outcome is described as analyzed among participants who completed at least one HIIT session, with the record stating that this group comprised 9 participants. This is an analysis-population definition based on starting the intervention. It is not the same as a complete account of adherence: the record does not say how many sessions each participant completed, how many intervals were completed in each session, or whether all scheduled observations were available. The distinction matters because an average based on sessions attended may not describe the experience of participants who did not begin training or who missed sessions.

What does variability mean for feasibility?

General statistical explanation: variability matters because the same average can arise from very different patterns. Participants might complete similar numbers of intervals, or some might complete many while others complete few. A mean and standard deviation can begin to describe these patterns, but distributions, participant-level trajectories, and attendance information can add context. Those details are not reported in the registry record. In feasibility research, the pattern of participation and the reasons for incomplete training can be important alongside an average endpoint.

What can the planning illustration establish?

The registry includes assumptions for a planning illustration based on an observed effect: a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. Such assumptions describe a hypothetical planning exercise, not the original single-group study design. The registry record does not report numerical planning results in the registry record for this analysis. Any participant counts from such an illustration would be planning quantities, not the number observed in this study, and not evidence that the study had a particular probability of detecting an effect.

General statistical explanation: a sample-size calculation depends on the effect size to be detected, the variability of the outcome, the chosen significance threshold, and the desired power, as well as the design and analysis. If a continuous outcome has greater variability than assumed, a given sample size generally yields less precise estimates. A calculation that uses a fraction of an observed effect is an illustrative scenario; it does not establish that the effect is reproducible or that the original study was designed around that scenario. The registry record does not report the original sample-size justification or a statistical analysis plan.

Why is over-dispersion relevant in general?

General statistical explanation: over-dispersion occurs when observed variation is greater than a statistical model assumes. A model that understates variation can make uncertainty appear smaller than it is. For a count-like endpoint such as completed intervals, the appropriate treatment of variation depends on how the observations were collected and modeled. The registry record describes a mean and standard deviation but does not report a model for the primary endpoint, a distributional assessment, or an adjustment for over-dispersion. It is therefore not possible to evaluate whether a particular count model or variance assumption was used.

The registry reports 10 outcome measures overall and names perceived exertion, adapted perceived exertion, and feelings during HIIT among the secondary outcomes. It does not report numerical findings for those named measures in the registry record. Statistical interpretation is consequently limited to the design and outcome definitions, rather than estimates of change or evidence about relationships among outcomes.

10. Multiplicity, Missing Data and Analysis Populations

The record lists 10 outcome measures overall and names perceived exertion, adapted perceived exertion, and feelings during HIIT among the secondary outcomes. It does not explain which outcomes were tested together, whether any outcomes were designated exploratory, or whether the analysis adjusted for multiple comparisons. A multiplicity procedure and the rationale for any such procedure are not reported in the registry record.

General statistical explanation: when multiple hypotheses are tested, the chance of at least one apparently unusual result can increase if each test is interpreted separately at the same threshold. Adjustment methods can address this issue, but may also affect the interpretation and precision of estimates. Without the analysis plan and results, the consequences of multiple outcome testing cannot be assessed for this study. The registry record also does not state whether outcome analyses were prespecified in detail or whether there were changes from an original plan.

The primary endpoint analysis included participants who completed at least one HIIT session, stated as 9. The record does not explain how missing observations were handled, whether all attended sessions contributed to the average, or whether participants with incomplete training had partial endpoint data. It does not report reasons for missing sessions or missing measurements, nor does it describe imputation or sensitivity analyses. These omissions limit assessment of how representative the analyzed observations are of the planned training experience.

There is no randomized comparison and no allocation to distinct arms. The record does not describe an intention-to-treat analysis or a separate per-protocol analysis. The named analysis population is participants with at least one completed session; how this population was selected in practice, and whether any other population was analyzed, are not reported in the registry record. The statistical analysis plan, including any interim analyses, is not reported in the registry record.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: pressure ulcer onset (10.0%), femur fracture from fall (10.0%).

The registry lists 2 serious adverse events in the HIIT group, with 10 participants at risk. The serious-event terms are pressure ulcer onset and femur fracture from fall, each reported as 10.0%. The registry also lists 0 other adverse events among 10 participants at risk and 0 deaths. These are the posted counts and percentages; they should be read as safety descriptions recorded for this study, not as comparative risk estimates.

The study had a single group and no control arm, so the serious-event figures do not provide a controlled comparison. The record does not report whether the events were judged related to HIIT, when they occurred relative to training, how they were managed, or whether they involved the same or different participants. The percentage attached to each listed term does not by itself show causation or establish the likely frequency of events in a broader population. With the registry’s limited safety details, interpretation should remain confined to the event counts and terms reported.

12. What the Result Does, and Does Not, Mean

The registry record describes a feasibility and acceptability study of arm-cycling HIIT for untrained manual wheelchair users with spinal cord injury or disease. It specifies a six-week program and a primary endpoint based on completed work and rest intervals. It also identifies the primary analysis population as 9 participants who completed at least one training session. These details clarify what the investigators intended to examine and whose interval-completion data were included in the primary analysis.

The record does not report the primary endpoint’s mean or standard deviation. It also does not give numerical results for the named secondary outcomes. As a result, the posted record does not establish the typical number of intervals completed, the variability of completion, or participants’ reported exertion and feelings during training. Feasibility and acceptability are the stated aims, but the numerical results needed to assess those aims are not reported in the registry record.

The study’s single-group design also sets a boundary on interpretation. It does not provide a randomized comparison with another training approach or a non-training group. Any observed experience in the HIIT group would describe that group under the study conditions; it would not by itself show how the same participants would have fared under a different approach. The study is not described as a test of comparative effectiveness.

The safety counts document 2 serious adverse events, along with 0 other adverse events and 0 deaths in the registry listing. The record does not establish whether either serious event was caused by the intervention. These counts should not be transformed into a claim that the program is safe or unsafe. They are a limited description of events recorded in a small, single-group feasibility study.

Accordingly, the registry record is informative about the trial’s population, intervention structure, analysis population, endpoint definition, and recorded serious events. It does not provide enough outcome detail to conclude whether the training goal was achieved, whether the program was acceptable, or how the outcome compares with another intervention. Absence of numerical outcome results is a limitation of what can be interpreted from this record, not evidence of a particular result.

13. Why This Trial Matters Statistically

Feasibility studies address practical questions that can shape later research: whether participants can undertake the intervention, whether outcome measures can be collected, and what aspects of the program may need refinement. This trial focuses on an exercise format adapted for manual wheelchair users with spinal cord injury or disease. Its interval-completion endpoint is directly connected to participation in the planned work-and-recovery structure, rather than to a comparison between treatments.

The registry makes the study’s single-group design explicit. That matters statistically because a feasibility measure and a comparative treatment effect answer different questions. A completion average could describe participation among those analyzed, but it would not estimate what would have occurred under a comparator. The distinction helps prevent a descriptive feasibility study from being interpreted as a controlled efficacy trial.

The primary analysis population is also important. The record specifies participants who completed at least one training session, numbering 9. That definition makes clear that the primary outcome analysis was not described as including only people who completed every scheduled session, nor does it indicate how people who never began were handled in other analyses. The record does not provide enough detail to assess the complete participant flow or adherence pattern.

For statistical interpretation, the missing numerical endpoint results are consequential. An endpoint definition and analysis population alone cannot show the observed level of completion or its variability. The registry’s safety counts add useful descriptive information, but without attribution and contextual detail they do not establish causality. Taken together, the record illustrates why feasibility conclusions require transparent reporting of participation, outcome summaries, missing observations, and adverse-event context—not only a stated protocol and endpoint.

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 principal limitation for interpreting results is that numerical findings for the primary endpoint are not reported in the registry record. The planned mean and standard deviation of completed intervals are absent, as are numerical results for the named secondary outcomes. This prevents assessment of the amount and consistency of training completed and the reported experience of participants.

The single-group design has no randomized or matched control group. It cannot support a direct comparison with another exercise program or with no intervention. The analysis population is limited to participants who completed at least one HIIT session, stated as 9, but the record does not explain the extent of attendance, the completion of individual sessions, or the handling of missing measurements. The number of participants who did not begin training is not described beyond the planned enrollment of 10 and the primary analysis group of 9.

The registry does not report a detailed statistical analysis plan, sample-size justification for the original study, interim analyses, multiplicity methods, or missing-data procedures. It does not provide participant-level results, distributions, or reasons for incomplete participation. The planned intervention schedule is described, but adherence to its specific targets is not reported.

Safety interpretation is limited by the absence of event timing, attribution, and further clinical context. The record lists serious-event terms and counts, but does not say whether the events were related to HIIT or whether they occurred in the same participant. These constraints mean that the registry record supports a narrow descriptive account rather than a comprehensive evaluation of feasibility, acceptability, or safety.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Feasibility of HIIT in Spinal Cord Injury — NCT03152110.
• Registry record last updated 2020-11-04; status last verified 2020-11.
• Results first posted 2020-11-04.
• 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.

18. Record Summary

This completed single-group study evaluated a six-week arm-cycling HIIT program for untrained manual wheelchair users with spinal cord injury or disease. Planned enrollment was 10. Sessions were scheduled 3 times per week, with 2 supervised sessions and 1 unsupervised session. The primary endpoint was the number of work and rest intervals completed per session, averaged over sessions and participants. The primary analysis population was stated as 9 participants who completed at least one training session.

The registry lists perceived exertion, adapted perceived exertion, and feelings during HIIT among secondary outcomes. It reports 2 serious adverse events among 10 participants at risk, with pressure ulcer onset and femur fracture from fall each listed as 10.0%; it also lists 0 other adverse events and 0 deaths. Numerical primary and secondary outcome results, event attribution, and details of missing-data handling are not reported in the registry record.