Mean Distance:

The mean distance is the mean of the resultant distance time series and represents the average distance from the mean centre of pressure.

A higher value in the AP direction usually indicates an ankle strategy for balance, while a higher value in the ML direction usually indicates more of a hip strategy.

Hip strategies for balance are less efficient when compared to ankle strategies and are often found in overweight people and commonly the elderly.

RMS:

The RMS is the root mean squared and represents the standard distribution of the data. The RMS tends to increase with age and any other factor that reduces balance.

Range:

The range is the maximum distance between any two points on the centre of pressure path.

The smaller the result the more consistent the persons sway pattern, however this test can be greatly changed if a sudden movement occurs.

This result tends to be higher in people with poor balance

Mean Velocity:

The mean velocity is the average velocity of the centre of pressure, and represents the speed of movement of the centre of pressure.

The closer this value is to 100% the better as slow reactions can be as detrimental as fast and is seen in poor tone states.

Aging tends to cause a higher value however as do things that increase general tone.

95% Confidence Ellipse:

The 95% confidence ellipse area is the area of the 95% bivariate confidence ellipse, which is expected to enclose approximately 95% of the points on the centre of pressure path.

The ellipse can be used to show general sway movements and directions of sway, and can sometimes help determine a semicircular canal involvement in the direction of sway.

Sway Area:

The sway area estimates the area enclosed by the centre of pressure path per unit of time.

Sway area is dependent on the distance from the mean centre of pressure and the distance travelled by the centre of pressure. Increases with poor balance.

Mean Frequency:

The mean frequency is the rotational frequency in revolutions per second or Hz, of the centre of pressure if it had travelled the total excursions around a circle with a radius of the mean distance. This measure is proportional of the mean velocity to the mean distance.

The mean frequency tends to increase with age however it can decrease in dopaminergic deficiency states.

Parkinsonian sway generally has a back left and forward right component with a decrease in sway frequency, however more evidence is required to use the frequency and direction to diagnose dopamine deficiencies.

Fractal Dimension:

The fractal dimension is a unitless measure of the degree to which a curve fills the metric space which it encompasses. This is used to determine the amount of error in the test and if patients are showing large values then it might be necessary to increase the testing time or that there is a problem with the patient causing them to have an inconsistent sway pattern where they range significantly rather than swaying around a certain point.

Balance Age:

The balance age is a cumulative score based on the above calculations that is used to give a relative age or score. This score is given as a relative balance age or physiological age (see physiological vs chronological age) This makes it an easy tool for comparing patients before and after and to track progress.

The best possible balance age in this program is 22 years old for both males and females.

The balance age score is used when comparing to the balance graphs to determine if a problem is associated with a loss of vestibular, proprioceptive or ocular function.

For example, if a patient is 30 years old has a balance age of 45 when they are tested with their eyes open on the hard surface, a balance age of 25 when they close their eyes, a balance age of 45 when they are open on the foam surface and then 25 again when they close their eyes on the foam surface. Then we can say that their balance is relatively IMPROVED when they close their eyes. When looking at the graphs in the appendix or the user start up guide you can see that this matches the graph of ocular loss. (i.e. the patient has a problem with their visual vertical or ocular map and therefore their balance is improved when this mismatch is removed.)

Falls Risk:

Falls risk is also calculated from the cumulative data but uses a different ratio to incorporate the increased risk with medial to lateral sway. The percentage risk given is a risk of falling per year for unknown causes (non-mechanical fall).

Adaption/Fatigue Ratio:

This is a measurement that compares the first half of the test to the second half.

Patients with an adaption ratio are improving during the test while a fatigue ratio indicates a decline in performance throughout the test. When giving home exercises it is recommended that they are exercises that incorporate situations that encourage adaption not that cause fatigue.