Peak Impact Forces and Metabolic Cost During Mid-Forefoot Striking in Shod Versus Barefoot Runners: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Peak Impact Forces and Metabolic Cost During Mid-Forefoot Striking in Shod Versus Barefoot Runners (NCT01536171), a registered phase not stated study. The primary outcome is Metabolic Rate During Barefoot and Shod Running.

2. Clinical Question

The clinical question is a comparison of physiological measurements under two running conditions, not a comparison of separate clinical treatments. The primary endpoint is metabolic rate, measured in kilojoules per minute. The registry description says each person runs for 20 minutes on two different days, once with shoes and once without them. It does not report the order in which conditions were completed or whether that order was assigned randomly.

The population is narrow by design: the brief description concerns people who already use a forefoot strike. Therefore, the question is not whether runners generally should change their gait or footwear. It is whether the recorded measures differ between these two conditions in the described group. The record does not report the observed metabolic-rate values, the estimated difference between conditions, or uncertainty around that estimate. It also does not report a result for peak impact forces. The study's stated question can therefore be described, but its empirical answer cannot be recovered from the registry record.

3. Trial Design

This is a completed experimental study sponsored by the University of Florida. The registry lists a start date of 2011-09 and primary completion in 2012-07. It describes two treadmill running conditions: normal running shoes and barefoot. The brief summary says participants already use a forefoot-strike gait and describes two test sessions. The primary outcome description specifies two visits, approximately 2 hours for each visit, and says each person runs for 20 minutes on the treadmill on two different days, once in each condition.

The record lists enrollment as 22, while the brief study description states N=20 and ages 18-45 years. These are different figures in the registry record, and it does not explain their relationship. The participant flow, including how many people completed both visits or contributed data to each outcome, is not reported in the registry record.

The study description indicates that the same person experiences both running conditions. This makes within-person comparisons a natural way to think about the intended measurement contrast: each participant's result in one condition could be compared with that participant's result in the other. However, the registry does not state the allocation method, order assignment, or whether condition order was randomized or counterbalanced. It also does not report a washout or other details about the interval between sessions. Those features should not be inferred.

The record identifies metabolic rate as the primary outcome and peak impact forces as a secondary outcome. It lists two outcome measures and no analyses. It does not report a statistical analysis plan, sample-size justification for the trial, analysis population, or participant-level results. The sample-size illustrations associated with the registry record are planning calculations, not evidence about the trial's observed statistical power.

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.

Population: Healthy young active adults

6. Primary Endpoint

The registry lists the primary outcome as Metabolic Rate During Barefoot and Shod Running, measured over Study consists of two visits, approximately 2 hours for each visit.

The primary endpoint is metabolic rate during barefoot and shod running, expressed in kilojoules per minute. Metabolic rate quantifies the rate at which the body expends energy during the activity being measured. In this study, it is used to compare the physiological cost of treadmill running under the two footwear conditions.

The registry identifies the outcome parameter as a mean and its dispersion as a standard deviation. A mean describes the average observed value within a condition. A standard deviation describes how spread out individual measurements are around that average; it is not the same as the uncertainty in the estimated mean or in a contrast between conditions. The endpoint description says each participant runs for 20 minutes in each condition on different days, but the registry does not report how the measurement period was summarized or which specific portions of a run contributed to the endpoint.

For a study in which participants undergo both conditions, the contrast of interest is ordinarily the within-person change or difference in metabolic rate between conditions. Pairing can account for stable differences between participants because each person serves as their own reference. That is a general statistical rationale, not a statement about the analysis actually used in this study. The analysis method is not reported in the registry record.

The record does not include observed means, standard deviations, a condition contrast, confidence interval, or p-value for metabolic rate. It also does not provide enough information to determine how precisely the primary endpoint was estimated. The endpoint's purpose is clear, but its measured result and comparative interpretation are not available in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical terms in the record describe the endpoint, but the registry does not identify the analysis method used. The explanations below are general and should not be read as a reconstruction of the study's analysis.

What does a mean and standard deviation describe?

For a continuous outcome such as metabolic rate, a mean gives the average of the measurements included in a condition. The standard deviation describes how much individual measurements vary around that mean. A larger standard deviation indicates more spread among the observations; it does not, by itself, mean that the mean is estimated less precisely by a particular amount. Precision also depends on how many observations contribute and on the structure of the data.

In a study with two measurements per participant, the distribution of the within-person differences may be especially relevant. The average of those differences represents the average contrast between conditions. The variation of the differences reflects how consistently participants' condition contrasts align. Separate condition means and standard deviations do not fully describe this within-person relationship.

Why does pairing matter?

When the same participants are measured in both conditions, observations from one participant are related. A paired analysis retains that connection by comparing each person's measurements across conditions. This can help distinguish a condition contrast from stable differences between participants. An analysis that treats the condition measurements as if they came from unrelated groups does not use the same information and may represent the design poorly.

Pairing does not resolve every design issue. Condition order may matter if running performance changes across sessions, and measurements may be influenced by factors that vary from one visit to another. The registry record does not report condition-order assignment or the analysis approach, so it is not possible to assess those issues for this trial.

What would an estimate and confidence interval add?

A contrast estimate expresses the size and direction of the observed difference between conditions. A confidence interval communicates the uncertainty around that estimate under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, but interpretation also depends on what values are scientifically meaningful. A confidence interval is not a guarantee that the true value lies within the particular interval, nor does it show the probability that a hypothesis is true.

The registry record does not report a contrast estimate or confidence interval for metabolic rate. No precision judgment can therefore be made from the endpoint labels alone. Standard deviations, even if they had been reported, would describe variability in measurements rather than directly supply uncertainty around the paired contrast.

What does a p-value address?

In general, a p-value measures how incompatible the observed data are with a specified null model, under the assumptions of the statistical test. It does not measure the size or importance of an effect, and it is not the probability that the null hypothesis is true. A p-value is most informative when considered alongside the estimated contrast, its confidence interval, the analysis plan, and the study design.

No p-value or analysis result is reported in the registry record. It would be inappropriate to infer statistical significance or the absence of a difference from the fact that the record lists an endpoint but no analysis.

How should the planning illustrations be read?

Sample-size planning uses assumptions about the effect to be detected, variability, the significance level, allocation, and the chosen statistical approach. The registry's planning note describes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. Those calculations are planning illustrations, not observed power and not evidence that the trial had a particular probability of detecting an effect.

The described measurements are from two conditions in the same people, while the planning note refers to equal allocation between two arms. A planning calculation based on that framing should not automatically be treated as a design-specific justification for a within-person comparison. The trial's own sample-size rationale is not reported in the registry record, and the record does not provide effect estimates with which to evaluate the illustrations.

Over-dispersion is a general concern for count outcomes when variability exceeds what a simple count model expects. It is not the central issue for the primary endpoint, which is a continuous metabolic-rate measure. For this endpoint, appropriate modeling depends on the continuous measurements, within-person structure, and assumptions about the distribution of the relevant contrast. The registry record does not specify the model or report checks of its assumptions.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists metabolic rate as the primary outcome and peak impact forces as a secondary outcome. Considering more than one outcome can create a multiplicity issue if several hypothesis tests are used to support a single overall claim. The chance of obtaining at least one apparently unusual result can increase as more tests are considered, depending on how the tests are related and how decisions are made. General approaches include prespecifying a primary test, adjusting for multiple comparisons, or interpreting secondary outcomes as exploratory. The registry record does not report a multiplicity strategy or a statistical analysis plan.

The record identifies two outcome measures but reports no analyses. It does not state whether the primary outcome was tested, how the secondary outcome was analyzed, or whether any additional comparisons were planned. There are no posted result estimates in the registry record with which to evaluate selective reporting or consistency between outcomes.

Missing-data handling is also not reported. The registry lists enrollment as 22, while the study description says N=20, and it does not explain the difference. It does not provide participant flow, the number completing both conditions, reasons for missing measurements, or the number included in each analysis. There is therefore no basis for judging whether missing data occurred or how it may have affected the results.

The analysis population is not reported in the registry record. In a repeated-condition study, the number with usable measurements from both sessions can matter for a paired comparison. The record does not say whether analyses used all enrolled participants, only completers, or another set of observations. These gaps prevent assessment of the planned analysis population and the handling of incomplete outcome data.

11. Safety Results

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

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 registry safety entry lists 22 people at risk in the serious adverse event category and 0 affected. It also lists 22 people at risk in the other adverse event category and 1 affected. These are the figures recorded for the group titled “Mid-Forefoot Striking in Shod Versus Barefoot Runners.” The record does not provide the term or description for the other event, and the list of top serious event terms is empty.

The serious and other adverse event categories are distinct entries; the figures should be read according to their labels rather than combined. The record does not describe how events were defined, how they were collected, or whether events were assessed as related to either running condition. It also does not give detail about severity or timing for the one other event.

Deaths are listed as null, which means deaths are not reported in the registry record; it should not be interpreted as a reported count of zero. More generally, these entries are a limited registry safety summary. They do not establish that no unlisted events occurred, and they do not permit a comparison of safety between conditions because the record does not give condition-specific event counts. The small study description and the absence of event detail also limit how much can be inferred from these figures.

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

The registry record documents a completed pilot study designed to measure metabolic rate and peak impact forces during treadmill running in shoes and barefoot. It gives the primary endpoint's unit and the broad schedule of the two visits. It also provides a brief description of the intended participant group. These registry entries clarify what the study set out to measure, but they do not provide the outcomes needed to answer whether the measures differed between conditions.

No observed means, standard deviations, effect estimates, confidence intervals, or p-values are reported in the registry record. As a result, the size, direction, and precision of any condition contrast are unknown. The record cannot support a conclusion that the conditions produced a difference, nor can it support a conclusion that they did not. Absence of posted results is not evidence of equivalence.

The study description concerns healthy runners who already use a forefoot-strike gait. Any findings, if available, would relate most directly to that described population and experimental setting. The registry does not provide enough detail to assess how participants were recruited or how representative they were. It also does not report the order of conditions or the statistical analysis used. Those details are relevant to understanding the comparison and its reliability.

The record's planning illustrations should be understood as hypothetical sample-size calculations based on stated assumptions. They do not show the study's observed power, and they do not reveal the actual outcome effect. A pilot label likewise does not establish a particular purpose or guarantee that an estimate is precise; the registry does not report a pilot-specific objective.

In practical terms, the record identifies a question and describes how the key measurements were intended to be collected. It does not contain a reported statistical answer. The serious adverse event entry records 0 affected among 22 at risk, while the other event category records 1 affected among 22 at risk, with no event description. Those entries should be read as registry safety figures, not as a complete assessment of comparative safety.

13. Why This Trial Matters Statistically

This study raises a statistical design issue that is common in laboratory and exercise research: the same participants may be measured under more than one condition. Such a design can be informative because each participant's measurements are connected. A clear analysis needs to preserve that within-person structure rather than treating the conditions as unrelated groups by default. The registry describes repeated conditions but does not report the analysis method, so the record also illustrates why design details and analysis details are both needed for interpretation.

The study is identified as a pilot, and its primary endpoint is a continuous physiological measure. Pilot studies can help establish whether procedures and measurements are feasible, but an estimate from a small study may be imprecise. The registry does not state the pilot's specific objective, its sample-size rationale, or its result estimates. Thus, the pilot designation alone cannot establish what the study was intended to demonstrate or how informative its measurements were.

Outcome reporting is central to statistical interpretation. An endpoint definition says what investigators intend to measure; it is not a result. Without condition-specific summaries and an estimate of the contrast, readers cannot assess magnitude or precision. The record's listing of no analyses makes this distinction especially important: the endpoint and design are described, but the statistical evidence is not reported.

The enrollment discrepancy in the record—22 listed as enrollment and N=20 in the brief description—also shows why participant flow and analysis populations matter. A transparent account would clarify who entered the study, who completed each condition, and who contributed to each endpoint. The registry does not provide that account. Taken together, the record is useful for identifying the intended comparison and measurement framework, while leaving the central statistical conclusions unresolved.

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.

Several trial-specific limitations follow from the registry record. First, it does not report outcome results or analyses. There are no metabolic-rate estimates, peak impact-force results, contrast estimates, confidence intervals, or p-values. The principal limitation for interpretation is therefore the absence of a reported empirical comparison.

Second, the record does not reconcile its enrollment figures. It lists enrollment as 22, whereas the brief description states N=20. It does not explain whether these figures refer to different stages of recruitment, eligibility, or analysis. Participant flow and the analysis population are not reported, so the number contributing to each endpoint is unknown.

Third, the description indicates that each person completes both conditions, but the order of conditions and allocation method are not stated. The interval and other procedural details between test sessions are also not described beyond the statement that the runs occur on two different days and the visits last approximately 2 hours each. These omissions limit assessment of potential period or order effects and of how closely the comparison reflects the intended within-person contrast.

Fourth, the outcome descriptions provide limited measurement detail. The registry states the unit, mean parameter, and standard-deviation dispersion for the primary endpoint, but does not report the precise calculation or measurement procedures. The secondary outcome is named as peak impact forces, without reported results or further detail in the record.

Finally, the registry does not report a statistical analysis plan, trial-specific sample-size justification, multiplicity approach, missing-data method, or assessment of model assumptions. The event entry also lacks a description of the one other adverse event and reports deaths as null rather than as a stated zero. These limitations do not establish that particular problems occurred; they define what cannot be assessed from the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Peak Impact Forces and Metabolic Cost During Mid-Forefoot Striking in Shod Versus Barefoot Runners — NCT01536171.
• Registry record last updated 2014-04-21; status last verified 2014-03.
• Results first posted 2014-04-21.
• 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

NCT01536171 is a completed experimental pilot study sponsored by the University of Florida, with a start date of 2011-09 and primary completion in 2012-07. It compares treadmill running in normal running shoes and barefoot among runners described as already using a forefoot-strike gait. The brief description specifies ages 18-45 years and N=20, while the registry lists enrollment as 22.

Metabolic rate, measured in kilojoules per minute, is the primary outcome; peak impact forces are listed as a secondary outcome. The description specifies two visits, approximately 2 hours each, and a 20-minute run in each condition on different days. The registry record does not report outcome analyses, effect estimates, participant flow, or the analysis population. It also does not state condition order or allocation method. The safety entry records 0 affected among 22 at risk for serious adverse events and 1 affected among 22 at risk for other adverse events; the other event is not described, and deaths are not reported.