A sway test is a balance assessment that measures how much your body moves while you stand still. It works by challenging the three sensory systems that keep you upright: vision, the vestibular system in your inner ear, and proprioception (your body’s ability to sense its own position in space). Clinicians use sway tests to detect balance problems from concussions, neurological conditions, aging, and musculoskeletal injuries.
How a Sway Test Works
Standing perfectly still sounds simple, but your body is constantly making tiny corrections to stay balanced. A sway test quantifies those corrections. By removing or altering sensory inputs, like closing your eyes or standing on an unstable surface, the test reveals which systems are compensating and which ones aren’t working properly.
When everything is functioning well, your visual system, inner ear, and the position sensors in your joints and muscles work together to keep you stable. Take one of those inputs away, and a healthy person can still compensate. Someone with a balance deficit will sway noticeably more, shift their feet, or fall.
The Romberg Test: The Classic Version
The oldest and most widely used sway test is the Romberg test, a neurological exam that’s been around since the 19th century. It’s straightforward: you stand with your feet together, arms at your sides, and eyes open for about 30 seconds while a clinician watches your stability. Then you close your eyes and hold the same position for 30 seconds to one minute.
A positive Romberg sign means you could stand steadily with your eyes open but lost your balance once your eyes were closed. “Loss of balance” includes increased body swaying, moving a foot to catch yourself, or actually falling. The test is considered positive if you can’t maintain an upright posture for 60 seconds with your eyes closed. A positive result points to a problem with proprioception or the vestibular system, since closing your eyes removes the visual backup those systems rely on.
The Balance Error Scoring System (BESS)
The BESS is a more detailed sway test commonly used in sports medicine, especially for concussion evaluation. It uses three stances: a double-leg stance with feet together, a single-leg stance on the non-dominant leg, and a tandem stance where one foot is placed directly behind the other in a heel-to-toe line. In all three, your hands stay on your hips and your eyes stay closed.
Each stance is performed twice: once on a firm surface and once on a foam pad, for six total 20-second trials. The foam pad destabilizes the surface under your feet, forcing your body to rely more heavily on the vestibular system. A trained observer counts “errors” during each trial, things like opening your eyes, lifting your hands off your hips, stepping out of position, or swaying beyond a certain point. More errors mean worse balance. Because it requires no equipment beyond a foam pad and a stopwatch, the BESS is popular on sidelines and in clinics that don’t have access to lab-grade tools.
Digital and Smartphone-Based Sway Tests
Newer sway tests use technology to remove the subjectivity of a human observer. Force plates, which are platforms embedded with pressure sensors, track the movement of your center of pressure as you stand. They can measure the path length, speed, and direction of your sway with high precision. In research comparing standing conditions, force plate measurements showed that sway velocity jumped dramatically when subjects stood on foam with their eyes closed (48.32 cm/s) compared to standing on a firm surface with eyes open (0.80 cm/s), illustrating just how much sensory deprivation affects stability.
Force plates are expensive and not portable, which led to the development of accelerometer-based tests. Platforms like Sway Medical use the accelerometer already built into a smartphone, held against the body, to measure postural sway. The system calculates a stability score on a 100-point scale, where 100 is perfectly stable and 0 is completely unstable. Research has found that accelerometer-based tests show the same general trends as force plates: stability decreases as sensory inputs are removed. The accelerometer approach is far cheaper and can be used anywhere, from a training room to a battlefield, though it measures trunk acceleration rather than center of pressure, so the raw numbers aren’t directly comparable to force plate data.
What Sway Tests Detect
Sway testing was originally developed for neurological assessment, and it remains a core tool for evaluating conditions that affect balance. In concussion protocols, a sway test serves as a baseline and comparison tool. Athletes often take a sway test before the season starts so that if they take a hit, clinicians can compare post-injury scores to their personal baseline rather than relying on population averages. Beyond measuring balance, some digital platforms also test reaction time, visual processing speed, impulse control, and memory to build a fuller picture of cognitive function after a head injury.
Traumatic brain injury patients, even those with mild balance problems, show measurably different sway patterns compared to uninjured individuals. The test is sensitive enough to pick up deficits that might not be obvious during everyday movement.
Sway testing also plays a role in fall risk assessment for older adults. Normative data from over 6,280 individuals shows that postural sway increases with age, with results varying by sex. Women tend to maintain better sway control than men, and this advantage becomes more pronounced in older age groups. These population norms allow clinicians to flag someone whose sway is unusually high for their age, signaling elevated fall risk before a fall actually happens.
Chronic low back pain is another condition linked to abnormal sway. People with clinical lumbar instability, a subtype of chronic low back pain involving excessive movement in the lower spine, show significantly increased path length, sway velocity, and total sway area compared to healthy individuals. This effect is amplified when vision is removed, suggesting that spinal instability impairs the proprioceptive signals the body needs to stay balanced. Researchers have linked this to impaired joint position sensing in the lower back.
What Your Results Mean
Sway test results are most useful when compared to something: your own baseline, population norms for your age and sex, or repeated measurements over time. A single score in isolation tells you less than the trend. For concussion management, the key question is whether your balance has returned to your pre-injury level. For fall risk screening, the question is whether your sway falls within a normal range for people your age.
Body size, interestingly, does not appear to significantly affect postural sway scores. Age and sex are the two main demographic factors, which simplifies how norms are calculated. If your results are abnormal, the pattern of which test conditions gave you trouble helps narrow down the cause. Struggling only when your eyes are closed suggests a proprioceptive or vestibular issue. Struggling on foam but not on firm ground points more toward problems with how your body processes surface information through your feet and joints.
Because sway tests are noninvasive and quick, they’re often repeated at intervals to track recovery from injury or to monitor the progression of neurological conditions. A score that’s improving over weeks suggests the brain and body are recalibrating. A score that plateaus or worsens can prompt a change in rehabilitation strategy.