Combined Application of Electrical Stimulated Antagonist Contraction During Walking (Walking Study): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Combined Application of Electrical Stimulated Antagonist Contraction During Walking (Walking Study) (NCT02730598), a randomized na study. The primary outcome is Change in Knee Extensor Strength Assessed by Isokinetic Dynamometer..

2. Clinical Question

The registry record frames the study around whether combining electrical muscle stimulation with walking can strengthen muscles around the knee while allowing exercise at a comfortable pace. The registered primary endpoint is change in knee extensor strength, measured with an isokinetic dynamometer and reported in Newton-meters. Knee pain, knee flexor strength, quality of life, and timed functional tests are among the listed secondary outcomes.

The comparison is between two active walking approaches: the Hybrid Training System (HTS), which uses stimulation while participants walk, and sensory transcutaneous electrical nerve stimulation (TENS) while walking. The registry does not describe a no-treatment or usual-care group. Therefore, the results address the difference between these two study groups, not the effect of either approach compared with no intervention.

The record describes a randomized, single-masked, parallel-group trial. It identifies women with frequent knee symptoms in the official title and lists knee osteoarthritis as the condition. Further eligibility details, including the diagnostic criteria used to define the study population, are not reported in the registry record. The results can therefore be interpreted for the enrolled study population as described in the record, but the record does not establish how closely that population represents people with knee osteoarthritis more broadly.

3. Trial Design

The study is registered as randomized, single-masked, and parallel-group, and its status is completed. Enrollment is listed as 28. The registry record identifies the University of Kansas Medical Center as sponsor, lists the study start as 2016-02, and gives 2017-01-20 as the primary completion date. Phase is listed as NA.

Participants were assigned to HTS or sensory TENS. Both group descriptions specify walking at a comfortable pace for 30 minutes while receiving the assigned stimulation. The record does not state how often the walking sessions occurred, how long the intervention period lasted, or what the single masking arrangement meant in practice. In particular, the masked party and the steps used to maintain masking are not reported in the registry record.

The primary endpoint is change in knee extensor strength assessed at baseline and 12-week follow-up. The record describes familiarization with the testing equipment and instruction on lifting technique before peak isokinetic knee extensor torque is measured. Secondary outcomes include knee flexor strength, knee pain measured with a visual analog scale and KOOS, quality of life measured with KOOS, and walking, chair-stand, and stair-climb times.

The posted primary outcome summaries report 10 participants in each group. The safety record lists 14 participants at risk in each group. These different denominators are both recorded, but the reason for the difference is not reported in the registry record. It is not possible to determine from these entries whether the difference reflects availability of endpoint measurements, analysis-population definitions, or another reason. The registry also does not describe the original sample-size justification or the statistical analysis plan.

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:

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 Change in Knee Extensor Strength Assessed by Isokinetic Dynamometer., measured over Baseline and 12-week follow-up.

The primary endpoint is change in knee extensor strength, measured with an isokinetic dynamometer and expressed in Newton-meters (Nm). The assessment is specified at baseline and 12-week follow-up. The record says participants would become familiar with the equipment and receive instruction on lifting technique before testing of peak isokinetic knee extensor torque.

In general, an isokinetic dynamometer measures force or torque during movement at a controlled speed. Knee extensor strength reflects the ability of muscles that straighten the knee to produce torque. Measuring change from baseline focuses the endpoint on how the recorded strength measure shifted over the follow-up period, rather than only comparing the groups' values at a single assessment. The general rationale for measuring strength is that it is a direct measure of muscle function and is relevant to the study's stated goal of strengthening muscles around the knee.

The registry reports least-squares means and standard errors for the primary outcome. A least-squares mean is a model-based group mean, but the model and any covariates used to obtain it are not reported in the registry record. The posted result therefore gives the estimated changes and their reported uncertainty, while leaving important details about the adjustment behind those estimates unspecified. The endpoint is a strength measure; it is not itself a direct measure of pain, quality of life, or daily function.

7. Results Posted in the Registry

• Transcutaneous Electrical Nerve Stimulation (TENS): mean 3.80 versus 9.60 on control; difference -5.80 (95% CI -66.27 to 54.67), standardized effect d = -0.08; z-test p = 0.851.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Change in Knee Flexor Strength Assessed by Isokinetic Dynamometer

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Transcutaneous Electrical Nerve Stimulation (TENS): mean 6.30 versus 9.30 on control; difference -3.00 (95% CI -14.12 to 8.12), standardized effect d = -0.24; z-test p = 0.597.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Transcutaneous Electrical Nerve Stimulation (TENS) and the control. The interval gives the range of effects that remain compatible with the data.

Change in Knee Pain Assessed by a Visual Analog Scale (VAS)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Transcutaneous Electrical Nerve Stimulation (TENS): mean -11.90 versus -14.90 on control; difference 3.00 (95% CI -66.79 to 72.79), standardized effect d = 0.04; z-test p = 0.933.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Transcutaneous Electrical Nerve Stimulation (TENS) and the control. The interval gives the range of effects that remain compatible with the data.

Change in Knee Pain Assessed by Knee Injury and Osteoarthritis Outcome Score (KOOS)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Transcutaneous Electrical Nerve Stimulation (TENS): mean -5.30 versus -5.40 on control; difference 0.10 (95% CI -3.82 to 4.02), standardized effect d = 0.02; z-test p = 0.960.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Transcutaneous Electrical Nerve Stimulation (TENS) and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes cover strength, pain, quality of life, and timed functional tasks. The numeric secondary results posted in the registry include knee flexor strength, pain measured by VAS, and pain measured by KOOS. The registry lists additional outcomes, including KOOS quality of life and walking, chair-stand, and stair-climb times, but results for those outcomes are not reported in the registry record.

Across the posted secondary summaries, the comparison intervals are broad in relation to their point estimates and include values on both sides of zero. This general pattern is consistent with limited precision rather than a clear, uniformly estimated separation between the groups. The scales and units differ across outcomes, so the estimates cannot be treated as interchangeable measures or combined informally into a single overall effect.

The secondary findings provide context for the primary strength comparison, but they do not remove its uncertainty. They measure related yet distinct aspects of knee symptoms and function. A pain score, a strength measure, and a timed task answer different questions; agreement or disagreement among them would not by itself determine the result on the primary endpoint. The unreported secondary results also mean the full pattern across all registered measures cannot be assessed from the registry record.

The reported secondary p-values are unadjusted, and the registry record does not describe a plan for controlling multiplicity. When several outcomes are examined, some results may appear unusual by chance even if no underlying effect exists. Without a stated hierarchy or adjustment strategy, an isolated secondary result should carry less weight than a prespecified primary result. Secondary outcomes can suggest questions for further study, but these posted summaries do not establish a broad or consistent effect across pain, strength, and function.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Change in Knee Flexor Strength Assessed by Isokinetic Dynamometer
• Change in Knee Pain Assessed by a Visual Analog Scale (VAS)
• Change in Knee Pain Assessed by Knee Injury and Osteoarthritis Outcome Score (KOOS)
• Change in Quality of Life (QOL) Assessed by Knee Injury and Osteoarthritis Outcome Score (KOOS)
• Change in 20-meter Walk Time.
• Change in 5-chair Stand Time.
• Change in Stair Climb Time.

9. Statistical Interpretation

10. Statistical Methods Explained

What does the group difference represent?

A mean difference expresses the estimated separation between group averages on the same outcome scale. In the primary comparison, the registry lists sensory TENS relative to HTS, with an estimate of -5.8 Nm. The sign indicates the direction under that comparison convention; it should not be read as a stand-alone judgment about clinical importance. Clinical interpretation also depends on the outcome scale, the uncertainty around the estimate, and the study context.

The reported group values are least-squares means. In general, a least-squares mean is an estimated mean from a statistical model and may account for specified features of the data. The model specification, included covariates, and handling of baseline values are not reported in the registry record. Consequently, the exact meaning of the adjustment cannot be reconstructed from the posted outcome summary alone.

What do standard errors and confidence intervals describe?

A standard error describes the statistical uncertainty in an estimated mean. It is not the same quantity as the spread of individual participants' measurements. A standard error is generally smaller when the estimate is more precise, although its size also depends on the variability in the data and the analysis. The registry reports standard errors for the primary least-squares means.

A confidence interval gives a range of values compatible with the data under the statistical procedure used. In general, a wider interval signals less precision than a narrower interval. For the primary between-group comparison, the interval runs from -66.27 to 54.67 Nm. Because that range crosses zero and includes values on both sides, the data do not resolve the direction of the group difference. The interval should be considered alongside the point estimate, not treated as a set of guaranteed values or as the probability that the true effect lies within it.

What does the p-value say?

The primary unadjusted p-value is 0.851. A p-value measures how unusual the observed data, or more extreme data, would be under a specified null hypothesis and analysis model. It is not the probability that the null hypothesis is true, and it does not measure the probability that a result occurred by chance. A large p-value does not establish equivalence or absence of an effect. In this study, it accompanies a wide confidence interval, so the central limitation is the imprecision of the comparison.

The p-value is labelled unadjusted. The registry record does not report a multiplicity correction or a prespecified hierarchy of tests. A p-value from an individual endpoint should therefore not be read as though it necessarily accounts for testing several outcomes or comparisons.

Why can over-dispersion matter?

General explanation: over-dispersion occurs when observed variability is greater than a statistical model assumes. When a model underestimates variability, standard errors can be too small and confidence intervals too narrow, making the evidence appear more precise than it is. The opposite problem, an overly conservative estimate of variability, can produce wider intervals. The registry record does not report a model-based dispersion assessment for this trial, so no conclusion about over-dispersion can be drawn from the posted summaries.

For continuous outcomes, variability in the individual measurements affects the uncertainty around group comparisons. The registry reports standard deviations for some secondary outcomes and standard errors for others. These summaries are not interchangeable. A standard deviation describes variation among observations, while a standard error describes uncertainty in an estimated mean. General statistical methods can use either, depending on the analysis and the information available, but the underlying model and data structure determine what is appropriate.

What can be inferred from the study design?

Random assignment is intended, in general, to make comparison groups similar on average with respect to measured and unmeasured characteristics. It does not guarantee that groups are balanced in a small study. The parallel-group structure means the assigned groups are compared over the study period rather than participants crossing through both interventions, as far as the registry design label indicates. The record does not provide the randomization procedure, allocation concealment details, or the identity of the masked party.

The registry reports baseline and 12-week follow-up for the primary endpoint. A change score compares follow-up with baseline, but the exact statistical method for the posted least-squares means is not stated. The record does not say whether the analysis used change scores directly, adjusted for baseline, or used another approach. Those choices can affect estimates and precision, so they cannot be assumed.

The number of participants with a posted endpoint result is smaller than the enrollment number. That observation alone does not establish why measurements are absent from the outcome summary. Missing measurements, exclusions, and analysis-population definitions are not described in the registry record. General methods for handling missing data depend on why values are missing and on the assumptions of the method; there is not enough information in the record to judge which assumptions, if any, were used.

How should the statistical evidence be combined?

The point estimate gives the central comparison, the confidence interval conveys its uncertainty, and the p-value gives a test statistic's compatibility with a null model. None should be interpreted in isolation. Here, the primary estimate is modest in relation to the width of its interval, and the interval permits materially different directions and magnitudes. This is a reason to describe the result as inconclusive about the size and direction of the group difference, not as proof of no difference.

The registry record does not report the trial's original statistical analysis plan, its sample-size justification, interim analyses, or a protocol for handling multiple outcomes. The planning illustrations associated with posted summaries use explicit assumptions, but those illustrations do not establish what the investigators planned when designing the trial. Details that are not reported cannot be filled in from the outcome values themselves.

11. Confidence Intervals and Precision

The primary estimate is -5.8 Nm for sensory TENS relative to HTS, with a 95% confidence interval from -66.27 to 54.67. The interval includes zero and allows values on either side of zero. This means the observed data do not precisely distinguish the direction of the group difference. The point estimate alone gives a single central value, but the interval makes clear that substantial uncertainty remains.

In general, a confidence interval reflects both the amount of information in the data and the variability of the outcome, together with the method used to calculate the interval. A narrow interval would constrain the plausible range more tightly; a wide interval leaves more possibilities compatible with the data. The primary interval is wide, so it does not support a precise estimate of the between-group difference.

The primary least-squares means are accompanied by standard errors of 10.8 for HTS and 28.9 for sensory TENS. These standard errors describe uncertainty in the estimated group means, not the dispersion of individual strength changes. The endpoint summary lists 10 participants per group. The record does not explain how these outcome denominators relate to the enrollment of 28 or to the safety denominators.

Confidence intervals do not indicate whether a difference would be important in practice. The registry record does not state a threshold for a clinically meaningful change in knee extensor strength. It also does not provide enough information about the analysis model to evaluate every assumption behind the interval. Precision is therefore limited both by the breadth of the posted interval and by the lack of reported analytic detail.

The interval should not be read as demonstrating equivalence: an equivalence conclusion requires an appropriate design and prespecified bounds, which are not reported in the registry record. Nor does an interval crossing zero show that no effect exists. It indicates that the posted comparison is compatible with a range of values, leaving the direction and magnitude uncertain.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not a total across arms and not a count of events. They are illustrations based on the observed effect, rather than the trial's own original design assumptions. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect equal to the stated fraction of the observed effect. The original sample-size justification and its assumptions are not reported in the registry record.

The 80% power column describes the planned number of participants per arm under which a study would have an 80% chance, under the planning assumptions, of detecting the selected effect using the specified test procedure. The 90% column describes a higher target chance of detecting that effect under those assumptions. These are planning quantities, not guarantees: actual study results remain subject to sampling variation, the true effect, and whether the assumptions are reasonable.

Rows based on 100%, 75%, and 50% of the observed effect ask about progressively smaller effects. Smaller effects are harder to distinguish from random variation at a fixed level of precision, so the planning figures rise as the target effect gets smaller. These illustrations use the observed effect as their reference, even though the primary estimate is uncertain and its confidence interval is wide. If the observed effect is not a stable estimate of the underlying difference, planning directly from it can be misleading.

These figures are not observed power. They do not describe the probability that this completed study detected an effect after seeing its results. Instead, they illustrate sample sizes under stated assumptions for a hypothetical study designed to detect specified fractions of the observed effect. They should not be taken as evidence about what enrollment the investigators originally planned or as a substitute for a prospective design calculation using a justified target effect and variance assumptions.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -5.800; pooled standard deviation σ = 68.987.
2. n = 2 × (1.96 + 0.842)² × 68.987² / -5.800² = 2,220.9, rounded up to 2,221 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -5.8                      # observed difference in means
sigma <- 68.9873176750626                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2730598)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 2,221 (80% power), 2,974 (90% power)
 75% of observed effect: n per arm = 3,949 (80% power), 5,286 (90% power)
 50% of observed effect: n per arm = 8,884 (80% power), 11,893 (90% power)
power.t.test: 2221.8 
Simulated power at n = 2,221 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary endpoint and multiple secondary outcomes, but a multiplicity strategy is not reported in the registry record. Multiplicity refers to the increased chance of obtaining at least one apparently notable result when many statistical tests are performed. Researchers may address this issue through a prespecified hierarchy, adjustment procedure, or other approach. The record does not state whether any such approach was used.

The comparison p-values are labelled unadjusted. They should therefore be understood as individual, unadjusted tests rather than as results known to account for the full set of outcomes. Without a documented plan, it is not possible to tell whether the primary endpoint was the sole confirmatory test, how secondary tests were intended to be interpreted, or whether any analysis was designated exploratory. No multiplicity-adjusted conclusion can be drawn from the registry record.

Missing-data handling is also not reported. The trial enrollment is listed as 28, while the posted primary and secondary outcome summaries list 10 participants per group and the safety record lists 14 at risk per group. These entries do not explain why the denominators differ. The registry does not state how many participants completed each assessment, why any outcomes may be unavailable, whether missing values were imputed, or whether the analyses included all randomized participants.

Analysis-population definitions are not reported. In general, an intention-to-treat analysis aims to analyze participants according to their assigned groups, while other approaches may use different inclusion rules. The registry record does not identify which population was used for the posted estimates. It also does not report exclusions after randomization or how adherence to the assigned walking approach was assessed. Those details matter when judging whether the estimates represent assignment to a study group or participation in the intervention as intended.

The original statistical analysis plan, interim analyses, and detailed model specifications are not reported in the registry record. Their absence does not show that the investigators did not have such procedures; it means their content cannot be assessed from this record. These gaps limit evaluation of selective reporting, missing-data assumptions, and the confirmatory status of the posted results.

15. 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 non-serious adverse event terms

The safety record lists 14 participants at risk in each group. It records 0 serious adverse events affecting participants in HTS and 0 in sensory TENS, with 0 deaths in each group. It also lists 2 participants with other adverse events in HTS and 1 in sensory TENS. These are the counts posted in the registry; they are not percentages, and no additional rate has been calculated.

Serious and other adverse events are separate categories in the record. The entry indicates that no serious adverse events were recorded as affecting participants in either group, while other adverse events were recorded in both groups. The registry does not list serious adverse event terms. It does not provide descriptions of the other events, their severity, timing, relationship to the intervention, or how events were collected.

The safety denominators differ from the participant counts listed for the primary endpoint, and the registry does not explain the difference. A count of zero recorded serious events does not establish that an intervention is free from risk. These figures describe the safety entries in this completed study and should be interpreted in light of the limited information about event definitions and follow-up.

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

The posted primary result is an uncertain comparison of change in knee extensor strength between HTS and sensory TENS. The estimated difference is -5.8 Nm for sensory TENS relative to HTS, but its 95% confidence interval runs from -66.27 to 54.67. Because the interval includes values on either side of zero and is wide, the study does not determine the direction or size of the difference precisely.

This is not evidence that the two approaches are equivalent. Equivalence requires a design that specifies acceptable bounds for differences and an analysis suited to that question; such bounds and an equivalence analysis are not reported in the registry record. Likewise, the result does not establish that either approach is ineffective. An imprecise estimate can be compatible with several possible underlying effects.

The comparison also does not answer whether HTS or TENS is better than no treatment, usual care, or walking without stimulation. The registry describes a comparison between two active walking groups, both receiving electrical stimulation. Any changes observed within a group cannot, on their own, separate the contribution of the intervention from other influences over time.

The study's registered goals include strength and pain, with other functional outcomes listed as secondary measures. The numeric secondary summaries do not provide a basis for a broad conclusion across every outcome, and some listed outcomes do not have results reported in the registry record. Unadjusted secondary findings also require caution because a multiplicity plan is not reported.

The record describes a completed randomized trial with enrollment of 28, but the posted endpoint summaries use smaller group counts and the reason is not stated. Details about missing data, analysis populations, intervention frequency, masking, and the statistical model are also not reported in the registry record. These limitations constrain how confidently the estimates can be generalized or compared with other settings.

In general, a trial can inform a question without settling it. Here, the posted data provide an estimate and uncertainty for the relative change in knee extensor strength, but they do not establish equivalence, superiority, a causal effect versus no intervention, or a treatment recommendation.

17. Why This Trial Matters Statistically

This trial illustrates why a point estimate should not be interpreted without its uncertainty. The primary comparison is reported as a single numerical difference, but the confidence interval spans a wide range on both sides of zero. Reading only the central estimate could overstate how much the data establish about the direction or magnitude of the group difference.

It also illustrates the distinction between a within-group change and a between-group comparison. Participants in both groups walked while receiving stimulation. The central study question reflected in the primary result is whether the groups differed, not whether either group's change can be attributed solely to its assigned approach. A comparison group that receives an active intervention answers a different question from a no-intervention or usual-care group.

The registry record contains planning illustrations derived from the observed effect, alongside the completed trial's outcome summaries. These are useful for understanding how a chosen target effect and planning assumptions relate to sample size, but they are not a record of the original design justification. Keeping prospective planning separate from calculations based on observed results is important because the observed effect is uncertain, especially when its confidence interval is wide.

Finally, the difference between enrollment, endpoint counts, and safety denominators shows why analysis populations and missing-data reporting matter. The record gives useful outcome and safety summaries, but does not explain these denominators or describe the analysis plan. Clear reporting of those details helps readers judge precision, bias risks, and the scope of conclusions in a randomized clinical study.

18. 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 posted primary outcome groups contain 10 participants each, while enrollment is listed as 28 and safety denominators are 14 per group. The registry record does not explain the differences. Without participant flow or analysis-population details, readers cannot establish why the endpoint counts are smaller or whether the posted comparison includes all randomized participants.

The study has a single primary strength endpoint at baseline and 12-week follow-up, but the registry does not report the statistical model behind the least-squares means. It does not state whether baseline adjustment or other covariate adjustment was used. The masking label is single, but which people were masked and how masking was maintained are not reported. Randomization methods and allocation concealment are also not described.

The intervention descriptions specify walking at a comfortable pace for 30 minutes with HTS or sensory TENS, but the frequency and duration of the walking program are not reported in the registry record. Adherence, changes in other care, and the details needed to reproduce the intervention are not specified. These omissions make it difficult to assess exposure to the assigned approaches or the conditions under which the results might apply.

Some registered secondary outcomes do not have posted results, and a multiplicity approach is not reported. The record also lacks a stated threshold for a clinically meaningful strength change. As a result, the statistical comparison cannot be translated into a conclusion about practical importance, and the complete pattern across registered outcomes cannot be evaluated.

The population description is limited to women with frequent knee symptoms in the official title and knee osteoarthritis as the condition. Detailed eligibility criteria and diagnostic requirements are not reported in the registry record. Generalization to people outside the enrolled study population is therefore uncertain. These limitations do not negate the reported estimates, but they narrow what the record can establish.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Combined Application of Electrical Stimulated Antagonist Contraction During Walking (Walking Study) — NCT02730598.
• Registry record last updated 2018-06-15; status last verified 2018-06.
• Results first posted 2018-06-15.
• 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.

22. Record Summary

The registry record describes a completed, randomized, single-masked, parallel-group study sponsored by the University of Kansas Medical Center. Enrollment is listed as 28, and the condition is knee osteoarthritis. The study compared HTS stimulation while walking with sensory TENS while walking; both group descriptions specify a comfortable pace for 30 minutes.

The primary outcome was change in knee extensor strength measured by isokinetic dynamometer from baseline to 12-week follow-up. The posted mean difference for sensory TENS relative to HTS is -5.8 Nm, with a 95% confidence interval from -66.27 to 54.67 and an unadjusted p-value of 0.851. The interval is wide and includes values on either side of zero, leaving the size and direction of the group difference uncertain.

The registry lists multiple secondary outcomes and safety counts, but does not report a multiplicity strategy, missing-data methods, analysis-population definitions, or the detailed statistical model. It also does not explain why endpoint and safety denominators differ. The result is best treated as an imprecise comparison between the two active walking approaches, not as evidence of equivalence or a comparison with no intervention.