Balancing is a complex function involving the coordinated effort of the nervous system, muscles, and sensory organs to maintain stability and equilibrium. Stability is achieved by keeping the body’s center of gravity—the point where weight is evenly distributed—within its base of support (the area beneath the body making contact with the surface). When the center of gravity moves outside this base, the body must make rapid adjustments to prevent a fall. Measuring this ability is a fundamental part of healthcare and performance training, offering insights into fall risk, rehabilitation effectiveness, and athletic potential.
Assessing Static Stability
Static stability assessment focuses on a person’s ability to hold a fixed, non-moving position with minimal sway. The Romberg Test is a foundational clinical assessment that evaluates balance when the base of support is narrowed by placing the feet together. The test is performed first with eyes open, and then the subject closes their eyes while an observer watches for excessive sway or loss of balance.
A positive Romberg sign—when a person is stable with eyes open but loses balance with eyes closed—suggests a problem with proprioception (the body’s sense of its own position). By eliminating visual input, the test challenges the somatosensory and vestibular systems to maintain postural control. The Sharpened Romberg Test is a more difficult variation, involving placing the feet in a heel-to-toe tandem position, further reducing the base of support.
The Single-Leg Stance (SLS) Test is another common tool for gauging static balance. The subject stands on one limb, usually with arms crossed over the chest or on the hips. Time is recorded until they touch the free foot to the ground or move the standing foot, reducing the base of support to the area of a single foot.
The time a person can maintain the single-leg stance generally decreases with age. The inability to hold this position for at least 5 seconds has been associated with an increased risk of injurious falls. These simple, time-based tests provide a quick, practical screening measure of foundational balance control.
Measuring Dynamic and Functional Mobility
Dynamic and functional mobility assessment measures balance during movement, reflecting stability while performing daily tasks. The Timed Up and Go (TUG) test is a widely used performance-based measure combining balance, gait speed, and functional mobility. The test requires the person to stand up from an armchair, walk three meters (about 10 feet), turn around, walk back, and sit down again.
Timing begins when the person is instructed to “Go” and stops when they are fully seated. A healthy older adult completes the TUG in under 10 seconds, while a time of 12 seconds or more suggests an increased risk of falling. This measurement provides insight into the speed and stability of transitions, such as sit-to-stand and turning, which are common moments for loss of balance.
The Berg Balance Scale (BBS) is a more comprehensive assessment consisting of 14 tasks that progress in difficulty, evaluating both static and dynamic balance. Each task is scored on a 5-point ordinal scale from 0 (unable to perform) to 4 (normal performance), with a maximum total score of 56. Tasks include:
- Reaching forward.
- Transferring from a chair.
- Standing with eyes closed.
- Standing on one foot.
A score below 41 on the BBS indicates an increased risk of falling, while scores between 21 and 40 suggest that walking assistance may be necessary. The BBS provides a detailed profile of a person’s ability to shift weight and maintain stability during various functional movements that mimic daily activities. Gait speed assessment, often measured over 10 meters, is another fundamental component of functional mobility, as slower walking speeds are closely linked to poor balance and higher fall risk.
Technology-Aided Quantitative Assessment
Advanced balance assessment employs technology to provide quantitative data, moving beyond observation and timing. Force plates are considered the gold standard, measuring the forces exerted by the feet on the ground. These specialized platforms precisely track the Center of Pressure (CoP), the point where the total ground reaction force is applied.
By analyzing the CoP trajectory, force plates quantify subtle postural sway, providing metrics like the total distance the CoP travels (excursion) and the average speed of its movement (mean velocity). Lower values for CoP mean velocity and the area covered by the CoP ellipse are typically associated with superior postural control. This posturography data can detect balance deficits too small to be noticed during simple clinical observation.
Wearable technology, particularly devices incorporating accelerometers, offers a more portable and cost-effective alternative to force plates. These small sensors, often placed on the lower back or limbs, measure the body’s acceleration forces in three dimensions. Accelerometers quantify postural sway by recording and processing the acceleration of body segments during standing or movement tasks.
This technology provides objective measurements with higher granularity than traditional tests, and it has been validated against gold standard systems. Wearable sensors can be integrated with functional tests like the TUG to collect more detailed data on movement dynamics. They are also being explored for continuous monitoring in home or clinical settings.