EVIDENCE LIBRARY
Can Alcohol Affect Standing Balance Even When Gait Measures Stay Similar?
Can alcohol change standing balance when walking measures show little difference? A force-plate study explains center of pressure, BrAC and limits of impairment inference.
Short answer: Yes. In a 2023 study of 30 young women, alcohol was associated with substantially longer and faster center-of-pressure movement during quiet standing, while most pressure-platform gait measures showed no statistically significant change at the studied breath-alcohol condition. One stride-length measure did change. The finding is about two specific biomechanical tasks—not proof that anyone walked normally, passed a field sobriety test, or was safe to drive.
Forensic interpretation often treats “balance” as though it were a single capability. It is not. Standing still with feet close together, walking across an instrumented platform, performing standardized field sobriety tasks, and controlling a vehicle place different demands on the nervous system. An outcome that changes in one task but not another does not make the results inconsistent; it defines what the experiment actually measured.
What is center of pressure, and what does a force plate measure?
Center of pressure (CoP) is the location of the resultant ground-reaction force beneath the feet. As a person adjusts posture to remain upright, the point moves. A pressure-sensing platform can record the track of those movements across time and derive numerical descriptions of postural control. It does not directly read alcohol concentration, brain function, subjective intoxication, legal impairment, or intent.
Two particularly useful standing outcomes are CoP path length, the total distance traveled by the recorded pressure point over the observation interval, and average CoP velocity, path length divided by recording time. Under otherwise comparable testing conditions, greater path length and velocity can indicate more postural corrections. The interpretation still depends on footwear, stance width, duration, platform settings, instructions, repeatability, and other conditions.
During walking, pressure trajectories occur while the feet repeatedly contact and leave the surface. Investigators can derive left-right symmetry, step variability, gait-line measures, walking speed, cadence, and stride length. These are not equivalent to the quiet-standing measurements, even when the same device records both.
What exactly did the 2023 alcohol-and-balance study test?
Gimunová, Bozděch, and Novák studied 30 women aged 20–30. Based on Alcohol Use Disorders Identification Test (AUDIT) questionnaire scores, 15 were classified as lower-risk drinkers (scores 3–6) and 15 as hazardous drinkers (scores 7–13). The investigators tested each participant first at a reported 0.00% breath-alcohol condition and again after alcohol consumption at a target reported 0.11% breath-alcohol condition.
Participants drank vodka mixed with orange juice over 30 minutes, with the amount set at 1.0 gram of ethanol per kilogram of body weight. Breath testing was performed with a handheld Dräger Alcotest 6820 at intervals after drinking. The second assessment was scheduled near the targeted breath reading on the descending part of the alcohol curve. This matters: the study used instrument-reported breath measurements and did not establish a corresponding directly measured venous blood alcohol concentration for each test.
For the static task, participants stood barefoot for 30 seconds on a Zebris pressure platform, with heels and big toes touching, trying to remain as still as possible. Two recordings were made in each condition; the investigators selected what they described as the clearer recording for analysis. Walking was evaluated on the instrumented platform as a separate dynamic task. This was neither a roadside standardized field sobriety testing validation nor a blinded, placebo-controlled clinical trial.
What changed during standing—and what did not change during walking?
The clearest result was the increase in CoP distance and movement velocity during quiet standing. These within-group differences met the authors’ multiplicity-adjusted significance criterion for the standing analysis (reported p = .001 in both AUDIT groups).
| Outcome and group | Reported sober condition | Reported alcohol condition | Interpretive limit |
|---|---|---|---|
| Standing CoP path length, lower-risk group | 280.02 mm | 510.01 mm | Greater recorded sway-path distance; not a clinical diagnosis. |
| Standing CoP path length, hazardous-use group | 297.58 mm | 514.02 mm | Similar direction of change; no demonstrated difference between AUDIT groups. |
| Standing CoP mean velocity, lower-risk group | 9.33 mm/s | 17.00 mm/s | Faster pressure-point travel during the specified 30-second stance. |
| Standing CoP mean velocity, hazardous-use group | 9.92 mm/s | 17.13 mm/s | Measured standing behavior; not the individual’s driving performance. |
| Gait “butterfly” pressure-trajectory variables | Multiple measures evaluated | No significant differences identified | A nonsignificant test does not prove no gait effects. |
| Gait stride length, lower-risk group | 126.53 cm | 133.30 cm | It increased and met the gait-adjusted cutoff (p = .004); do not say every gait outcome was unchanged. |
Among the gait-pressure measures, the authors did not identify statistically significant changes in their butterfly-diagram outcomes. They did report longer stride length in the lower-risk group, with p = .004 against a gait-adjusted significance criterion of .005. Other isolated unadjusted-looking differences should not be promoted as significant when they did not satisfy the prespecified correction. The proper summary is narrower than “alcohol did not affect walking”: the measured static and dynamic outcomes responded differently in this small, specified experiment.
Why can quiet stance change when some gait metrics do not?
Quiet standing on a narrow base of support demands ongoing corrections to maintain upright posture. An instrument can detect changes in the path of ground pressure that may be difficult to recognize simply by watching. Walking, in contrast, is a patterned, dynamic movement with momentum, step-to-step adjustments, and different variables. A device’s failure to detect a significant difference in a chosen gait variable is not proof that every component of locomotor control or every clinically relevant function is intact.
The study does not isolate one neural structure or prove a particular molecular mechanism. Its CoP findings are compatible with alcohol affecting postural control under the tested conditions, but a force plate cannot distinguish cerebellar changes, vestibular contributions, attention, fatigue, or other physiological pathways without further measurements. Avoid attributing the observed pressure traces to one mechanism simply because alcohol can act on several systems.
Does a normal-looking walk rule out alcohol-related balance changes?
No such conclusion follows from this study. The researchers did not ask blinded observers to judge who “looked sober,” and they did not calculate the sensitivity or specificity of a visual walking assessment. Their numerical gait outcomes were collected under one protocol with a small number of participants. Moreover, at least one reported stride-length measure differed significantly between conditions. The study instead demonstrates that a static instrumented balance outcome may change when selected dynamic outcomes do not meet a significance threshold.
Consequently, it would be incorrect to use this article to claim either that an apparently steady walker has no alcohol-associated effects or that every person with a high breath-alcohol reading must show a visibly unsteady gait. Whether a specific person performed normally must be evaluated using the actual observations and their quality—not guessed from a group average.
Does a measured breath-alcohol concentration prove a particular degree of impairment?
A breath alcohol instrument reports alcohol under its validated sampling and calculation conventions; it does not measure force-plate sway, visual tracking, divided attention, reaction to hazards, or driving. In this experiment breath readings were used to define a controlled exposure condition; the CoP platform separately quantified postural behavior. The measurements may be compared as group research, but one cannot mathematically convert a CoP path length of 510 mm into an individual’s blood BAC, performance grade, criminal culpability, or crash causation.
For additional method context, the site’s Alcohol & Volatiles evidence guides distinguish analytical alcohol findings from interpretation, and its Pharmacology & Interpretation resources explain why a concentration is not itself an individualized effect measurement.
What does the study say about drinking history or tolerance?
When investigators compared the two AUDIT-defined groups, they did not find significant between-group differences in their tested stance or gait variables under the sober or intoxicated conditions. But a nonsignificant comparison among 15 people per group does not establish that drinking history never modifies alcohol response. Questionnaire-based classifications are not validated individual tolerance measurements, and no estimate of sensitivity to tolerance effects was established for forensic use.
The experiment was restricted to young women. It cannot settle how effects compare in men, older adults, people with vestibular or neurologic disease, those wearing different shoes, or individuals tested during a roadside stop. It also offers no reliable lower or upper BrAC threshold at which a particular visible sign will always emerge.
What should an attorney or toxicologist ask before applying these findings?
The foundational questions concern the actual testing conditions and the inference being proposed. Was the task quiet standing, instrumented gait, heel-to-toe walking, or an official standardized test? Were measurements quantitative or qualitative? What were the footwear, surface, stance width, timing, and instructions? Was ethanol measured by breath, blood, or something else, and when was that measurement taken relative to the behavior? Are injury, medical conditions, drugs, fatigue, training, and recording quality independently addressed? A study about average pressure-point motion cannot substitute for these case-specific facts.
This article is especially relevant when an argument assumes that all balance measures should agree or that one normal observation refutes another. The study supports a more disciplined proposition: different functional tests capture different aspects of performance, and their limitations must travel with the conclusions.
Frequently asked questions
What is the difference between postural sway and gait?
Postural sway is the small corrective movement involved in keeping balance during a standing task. Gait involves repeated steps and dynamic movement. A center-of-pressure recording can describe either, but the chosen outcome variables and their meanings differ.
Did the study find no alcohol effects on walking?
No. Most specified pressure-trajectory gait outcomes were not significant, but stride length increased significantly in the lower-risk AUDIT group. The results do not justify the blanket statement that all gait performance remained unaffected.
Is a force-plate test the same as a field sobriety test?
No. The study used a Zebris pressure platform to derive quantitative standing and walking measures. It did not validate roadside walk-and-turn, one-leg-stand, or horizontal gaze nystagmus performance, nor did it establish their diagnostic accuracy.
Was the reported 0.11% value a laboratory blood alcohol result?
No. The investigators specified a breath-alcohol condition and used a handheld breath instrument during the protocol. The study does not provide direct laboratory blood-alcohol results establishing each participant’s venous blood concentration at testing.
Can a negative gait finding demonstrate that someone was unimpaired?
No. Lack of statistical significance for a particular measured gait outcome does not prove global unimpaired functioning, and the study did not test actual driving or calculate individual diagnostic accuracy.
Did hazardous drinkers demonstrate alcohol tolerance?
Not as an established individual conclusion. The study found no significant differences between small AUDIT-based groups on the selected measurements, but it was not designed to certify or exclude tolerance in any named person.
Can these group averages establish why a fall or collision occurred?
No. They describe responses under the experimental protocol. Event causation requires independent assessment of conduct, medical and environmental alternatives, chronology, available recordings, measurement validity, and other relevant evidence.
Primary scientific reference
Gimunová M, Bozděch M, Novák J. Centre of pressure changes during stance but not during gait in young women after alcohol intoxication. PeerJ. 2023;11:e16511. doi:10.7717/peerj.16511. The paper is available as open full text at PubMed Central.
Scientific scope: This is an educational interpretation of one identified experimental study, not an individualized diagnosis, standardized field sobriety validation, legal opinion on a particular case, or independent proof of crash or injury causation. Study outcomes should not be generalized beyond their design without corroborating evidence.