Blood Flow Restriction Training (BFR) in an Adolescent Population: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Blood Flow Restriction Training (BFR) in an Adolescent Population (NCT04285879), a non-randomized na study. The primary outcome is Isometric Quad Strength Peak Torque.

2. Clinical Question

The clinical question is whether BFR exercise, used alongside a standard ACL protocol, is associated with differences in strength after ACL reconstruction in adolescents. The primary endpoint is isometric quadriceps peak torque, expressed in Nm/kg, with assessments described at 3 month and at return to sport post-operative strength (6-8 months post-op). The record also frames the study as examining strength, hypertrophy, functional outcomes, and patient-reported outcomes. It names Pedi-IKDC as a secondary outcome, but does not provide its results.

The comparison is not randomized. The registry record characterizes the non-BFR participants as prospective controls who were not receiving physical therapy at Connecticut Children's. This is important to the question: the groups may differ in ways other than BFR exposure, and the record does not report methods to adjust for such differences. The study can therefore describe outcomes in the groups, but a group contrast alone cannot establish that BFR caused any observed difference.

The record does not report numerical results for the primary endpoint, the size or direction of any group contrast, or uncertainty around a contrast. It therefore does not establish whether strength differed between groups. The question is clinically specific, but the available registry information does not supply the outcome data needed to answer it statistically.

3. Trial Design

The registry record describes a completed, parallel, non-randomized study with no masking. Its title identifies the topic as blood flow restriction training in an adolescent population, and its summary places the intervention in the context of ACL reconstruction rehabilitation. The listed sponsor is Connecticut Children's Medical Center. The record gives the study status as completed.

Patients in the BFR Exercise Group were to use BFR-based exercise in addition to the standard ACL protocol. The intervention listing names the Delfi Personalized Tourniquet System, and the arm description refers to the Owen Recovery Science exercise protocol. The comparator is called the Non-BFR Exercise Group. The record describes this group as prospective controls who were not participating in physical therapy at Connecticut Children's but had undergone ACL reconstruction by Elite Sports Medicine. This comparator differs from a randomized, concurrently assigned control group and should not be interpreted as a like-for-like comparison.

The record reports enrollment of 47 patients. It also states that exclusion criteria, loss to follow-up, and the COVID-19 pandemic meant that the investigators were unable to fully analyze all consented patients in both groups. It does not provide the number analyzed for the primary endpoint, the endpoint-specific group sizes, or a participant flow accounting for exclusions and missing follow-up.

The primary outcome is isometric quadriceps peak torque, measured by an isokinetic dynamometer on the involved and uninvolved limb. The record specifies measurement at 3 month and return to sport post-operative strength (6-8 months post-op). Pedi-IKDC is listed as a secondary outcome. The record lists five outcome measures but does not identify the other secondary measures in the available description. It does not report randomization, masking, an analysis plan, or a sample-size justification. The non-randomized design and incomplete analysis are central to interpretation: the registry record does not support treating the groups as exchangeable or assuming that every enrolled patient contributed to each outcome.

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: We enrolled 47 patients in our study. Due to exclusion criteria, patients lost to follow up and COVID-19 pandemic we were unable to fully analyze all consented patients in both groups.

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 Isometric Quad Strength Peak Torque, measured over 3 month and return to sport post-operative strength (6-8 months post-op).

The primary endpoint is isometric quadriceps strength peak torque. The record describes testing with an isokinetic dynamometer and measurement on both the involved and uninvolved limb. Results are intended to be expressed in Nm/kg, and the record specifies assessments at 3 month and at return to sport post-operative strength (6-8 months post-op). It identifies the summary measure as a mean with standard deviation.

Peak torque is a measure of the maximum torque generated during an isometric contraction. As a general statistical and measurement concept, an isometric test assesses force generation while the joint angle is held fixed rather than moving through a range. Recording the involved and uninvolved limbs permits strength to be described for each limb, although the registry record does not state how the limb measurements were combined or which comparison was used for the primary analysis.

Strength is relevant to the study's stated rehabilitation question because the investigators aimed to evaluate whether adding BFR exercise to traditional physical therapy improved strength after ACL reconstruction. The record also names functional and patient-reported outcomes as broader interests, but the primary endpoint is a strength measure rather than a direct measure of function or patient experience. Pedi-IKDC is listed as a secondary outcome.

The registry record does not report observed means, standard deviations, group contrasts, confidence intervals, or p-values for this endpoint. It also does not specify whether the primary inference concerns a particular visit, change over time, limb contrast, or group-by-time contrast. Without those details and outcome results, the endpoint definition can be described, but the magnitude and precision of any group difference cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods answer different questions: what was measured, how groups were compared, how much uncertainty surrounds an estimate, and which participants contributed to an analysis. The registry record describes the primary measure and some aspects of design, but does not report the statistical analysis methods used for the primary or secondary outcomes. The concepts below are general explanations, not claims about methods used in this study.

What does a mean describe?

The primary endpoint is described as a mean of a continuous measure, with standard deviation as its dispersion measure. A mean is the arithmetic average of observed values in the analysis group. The standard deviation describes how spread out individual observations are around that average. It is not the uncertainty in the mean itself. Estimating uncertainty in a mean or group contrast requires information about the observations and analysis approach, and the registry record does not report those results for the primary endpoint.

The endpoint is peak torque expressed in Nm/kg. In general, expressing a measure relative to body mass can aid interpretation across people of different sizes, but the record does not explain how the value was calculated beyond identifying the unit. It describes testing of the involved and uninvolved limb, without specifying how limb results were used in the statistical comparison.

What would a group contrast mean?

A group contrast summarizes how an outcome differs between groups under a defined analysis. For example, a contrast might compare average strength at a visit, or compare change over time. These are not interchangeable questions. The registry record names assessment times but does not state which contrast was the primary statistical target. It also does not report a contrast estimate. Without the estimand—the precise quantity the analysis aims to estimate—and the corresponding data, readers cannot infer what a reported group difference would represent.

A confidence interval is a range of values compatible with the data and the assumptions of the statistical model, expressed at a stated confidence level. It conveys precision as well as direction and magnitude. A narrow interval indicates greater precision than a wide interval, while an interval that includes no difference may be consistent with a range of effects. The registry record does not report a confidence interval or a significance threshold for the outcome analysis, so no conclusion about statistical precision can be drawn from it.

Why does non-randomization matter?

Random allocation is a design method that helps balance prognostic characteristics between groups on average. In a non-randomized study, group membership may be related to characteristics that also predict outcomes. As a general statistical issue, this is confounding: an observed group difference may reflect both the intervention and differences between the people receiving each approach. Statistical adjustment can sometimes address measured confounders, but cannot guarantee removal of bias from unmeasured or poorly measured factors. The registry record does not report an adjustment model or covariates used in an analysis.

The comparison described in this record has an additional practical distinction: the non-BFR group is described as not participating in physical therapy at Connecticut Children's. That makes the comparator different in rehabilitation context, not only in BFR use. No statistical method can make that difference disappear automatically. Readers should avoid interpreting a possible group contrast as the isolated effect of BFR unless the analysis and assumptions justify that interpretation; those details are not reported in the registry record.

How should missing outcomes be considered?

The record explicitly notes exclusion criteria, loss to follow-up, and the COVID-19 pandemic as reasons all consented patients could not be fully analyzed in both groups. Missing outcome data can reduce precision and can introduce bias when the chance of having an observed measurement is related to the outcome or to group membership. Complete-case analysis, imputation, and likelihood-based approaches make different assumptions. The registry record does not report which approach was used, how much outcome data were missing, or whether missingness patterns differed across groups.

Enrollment is not the same as the analysis population for a particular endpoint or visit. Some enrolled participants may not meet analysis criteria or may lack a measurement at a given time. Because endpoint-specific denominators are not reported, the number enrolled cannot be used to infer how many observations contributed to a mean or comparison.

What do planning calculations represent?

Sample-size illustrations based on an observed effect are planning scenarios. They show how a hypothetical future design might be sized under stated assumptions; they do not recover the study's planned sample size, and they are not observed power. The record says such illustrations use a two-sided significance level of 0.05, equal allocation, a normal approximation, and a stated fraction of the observed effect. It also distinguishes planning counts per arm from total event counts for time-to-event settings. These assumptions describe the illustrations, not necessarily the study's design or its analysis.

Observed power is not a substitute for a confidence interval or an effect estimate. Once results are observed, precision is better understood by examining the estimated effect and its uncertainty. Since the record does not report primary outcome estimates, a planning illustration cannot establish the strength or reliability of a treatment comparison in this study.

What is not documented?

The registry record does not report the primary outcome model, a sample-size justification, interim analyses, a prespecified statistical analysis plan, multiplicity adjustment, or an endpoint-specific analysis population. It lists five outcome measures and no analyses in the record's analysis listing, but does not provide outcome estimates. Those omissions do not prove that no methods were used; they mean that the methods are not reported in the registry record. Readers should distinguish a study's design description from evidence about how its results were analyzed.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists five outcome measures, names isometric quadriceps strength peak torque as the primary outcome, and lists Pedi-IKDC as a secondary outcome. It does not give results for these measures or identify all the secondary outcomes in the available description. The record also does not report how many statistical tests were conducted, which outcomes were included in each analysis, or whether any adjustment for multiple comparisons was used.

As a general statistical matter, examining multiple outcomes, time points, limbs, or group contrasts creates multiple opportunities to find an apparently unusual result. Multiplicity procedures can help control the chance of false-positive findings across a defined family of tests. They are not always required in the same way for every study, but the testing strategy should be clear to readers. The registry record does not report a multiplicity plan, so it is not possible to assess how the study handled this issue.

Missing data are a separate concern. The record states that exclusion criteria, loss to follow-up, and the COVID-19 pandemic prevented full analysis of all consented patients in both groups. It does not report endpoint-specific numbers analyzed, reasons for missingness by group, or the method used to handle missing measurements. These details matter because available-case results can be biased if observed participants differ systematically from those without measurements.

The registry record also does not define the analysis population for the primary endpoint or report whether participants were analyzed according to a prespecified group definition. It does not report a statistical analysis plan or an approach to handling repeated assessments. Without these details, readers cannot determine how the primary analysis was selected, whether all planned comparisons were reported, or how missing observations affected estimates. These methods are not reported in the registry record; their absence from the record should not be mistaken for proof that no analysis was performed.

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.

The registry record reports serious adverse events for the BFR Exercise Group with 33 at risk and 0 affected, and for the Non-BFR Exercise Group with 14 at risk and 0 affected. It reports other adverse events with 33 at risk and 0 affected in the BFR group, and 14 at risk and 0 affected in the non-BFR group. Deaths are reported as 0 in each group. These are the registry's recorded counts.

A zero count means no event was recorded in the listed category for the reported group. It does not establish that the underlying risk is zero, nor does it prove that the groups have equivalent safety. As a general statistical principle, sparse or zero-event data provide limited information about the range of event rates compatible with the observations. The registry record does not provide uncertainty intervals for these counts, event definitions, details of active surveillance, or group-specific follow-up duration.

The at-risk counts in the safety record should not be treated as endpoint-specific sample sizes for strength or other outcomes. The primary outcome analysis population is not reported. Safety counts are descriptive and cannot replace a comparative safety analysis, particularly in a non-randomized study with potentially different group characteristics and incomplete follow-up. The record does not report the most frequent serious adverse event terms.

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

The registry record establishes that this completed study examined BFR exercise alongside ACL rehabilitation in adolescents and identifies isometric quadriceps peak torque as its primary outcome. It also describes a non-BFR group and reports safety counts. These registry entries clarify the study question and design, but they do not provide the primary endpoint results. No group means, standard deviations, contrasts, confidence intervals, or p-values are reported in the record information.

Accordingly, the statistical evidence in the registry record does not show whether measured quadriceps strength was higher, lower, or similar between the groups. It does not establish the magnitude of any difference or its precision. The absence of outcome estimates is not a finding of no effect and should not be interpreted as proof that the groups had identical outcomes. Nor can the listed enrollment figure establish how many participants contributed to a specific endpoint or assessment time.

Even if a group difference were reported, the design would limit causal claims. Allocation was non-randomized, and the comparator group is described as not receiving physical therapy at Connecticut Children's. Differences in who entered each group, rehabilitation exposure, or other factors could contribute to a measured contrast. The record does not report adjustment methods that would allow these issues to be evaluated.

The safety record reports no adverse events in the listed categories, but that does not establish absence of risk or equivalence between groups. The event counts are descriptive, and the registry record does not provide the information needed to assess event ascertainment or precision.

The study's stated aims include strength, hypertrophy, functional outcomes, and patient-reported outcomes. Pedi-IKDC is listed as a secondary outcome, but results for it and the other listed outcome measures are not reported in the registry information. The record therefore supports a careful description of the research question and its limitations, not a conclusion about efficacy or clinical benefit.

13. Why This Trial Matters Statistically

This study is statistically notable for the gap between a focused clinical question and the limits of the available outcome reporting. It asks whether BFR exercise added to ACL rehabilitation relates to strength in adolescents, a population the registry summary describes as having limited information about BFR use. The primary endpoint is a defined, continuous measure, but the registry record does not report the observed values or statistical comparison needed to evaluate the question.

The non-randomized design also illustrates why the structure of a comparison matters. A group difference is not automatically an intervention effect. The comparator is described as patients who were not participating in physical therapy at Connecticut Children's, so BFR exposure is not the only stated distinction between the groups. This creates a need for careful consideration of confounding and comparability. The registry record does not report how those concerns were addressed statistically.

Incomplete analysis is another central feature. The investigators state that exclusion criteria, loss to follow-up, and the COVID-19 pandemic prevented full analysis of all consented patients in both groups. Without endpoint-specific analysis counts and missing-data methods, readers cannot assess how much information was available or whether missingness could have affected the results.

The safety counts provide a further lesson in interpretation: zero recorded events are descriptive, not proof of zero risk. Without event definitions, follow-up details, and precision estimates, those counts cannot establish comparative safety.

Finally, planning illustrations should be separated from observed results and from the study's own design. A calculation based on an observed effect can help illustrate assumptions for future planning, but it does not show that the study was adequately powered or validate a finding. In this record, the statistical lesson is primarily about distinguishing a clearly stated endpoint from the missing estimates and methods required to draw an outcome-based 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 principal limitation for interpreting outcomes is that the registry record does not report numerical results for the primary endpoint. Without group summaries or an estimated contrast, the direction, magnitude, and precision of a strength difference cannot be assessed. Results for the secondary outcomes are also not reported in the record information.

The allocation is non-randomized and unmasked. The non-BFR group is described as prospective controls who were not participating in physical therapy at Connecticut Children's but underwent ACL reconstruction by Elite Sports Medicine. This comparator may differ from the BFR group in care context or other characteristics. The registry record does not report baseline characteristics or adjustment methods, so the degree of group comparability cannot be assessed.

The record states that exclusion criteria, loss to follow-up, and the COVID-19 pandemic prevented full analysis of all consented patients in both groups. It does not provide endpoint-specific denominators, a participant flow account, missing-data patterns, or the method used to handle missingness. This prevents evaluation of how exclusions and incomplete follow-up affected precision or potential bias.

The primary endpoint description names more than one assessment time and measures both involved and uninvolved limbs, but the record does not specify which visit or contrast was the primary statistical target. It does not report the statistical model, analysis population, multiplicity plan, sample-size justification, interim analyses, or a prespecified analysis plan. These details are not reported in the registry record.

The safety entry is limited to event counts and at-risk counts. Event definitions, ascertainment procedures, duration of follow-up, and uncertainty estimates are not reported. Together, these limitations mean the registry information is insufficient for judging the size or reliability of outcome differences or making a causal interpretation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Blood Flow Restriction Training (BFR) in an Adolescent Population — NCT04285879.
• Registry record last updated 2024-07-17; status last verified 2024-07.
• Results first posted 2024-07-17.
• 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

NCT04285879 is a completed, parallel, non-randomized study titled “Blood Flow Restriction Training (BFR) in an Adolescent Population,” sponsored by Connecticut Children's Medical Center. The study evaluates BFR-based exercise alongside traditional ACL reconstruction rehabilitation in adolescents. The intervention listing names the Delfi Personalized Tourniquet System, and the BFR arm description refers to the Owen Recovery Science exercise protocol.

The primary outcome is isometric quadriceps strength peak torque, reported as a mean with standard deviation and measured in Nm/kg on the involved and uninvolved limb. Assessment timing is described as 3 month and return to sport post-operative strength (6-8 months post-op). Pedi-IKDC is listed as a secondary outcome. The record reports enrollment of 47 patients and states that exclusion criteria, loss to follow-up, and the COVID-19 pandemic prevented full analysis of all consented patients in both groups.

The registry record reports zero serious adverse events, zero other adverse events, and zero deaths in the listed groups. It does not report primary outcome estimates, a statistical analysis plan, endpoint-specific analysis populations, or methods for missing data. The non-randomized comparison and incomplete analysis constrain interpretation; the registry information does not establish an outcome difference or a causal effect.