Postural control is often associated with balance, since it involves maintaining, achieving or restoring this state of stability during any posture or static or dynamic activity. From a mechanical point of view, an object is balanced when its centre of mass (COM) lies on a vertical line that passes through its support base. Stability increases when the strength necessary to disrupt it also increases. These principles apply to the human body as well: when standing upright, the COM is in a relatively high position compared to the limited support base provided by the feet. In the case of an inanimate object, this condition would cause it to move or fall, whereas the human body, through postural control, has the intrinsic ability to use muscle activity to counteract gravity.
Postural control is a prerequisite for maintaining various postures and activities linked to three broad classes:
- Maintaining a specific posture;
- Voluntary movement;
- Reaction to an external disturbance.
There are many postural control strategies, which can be either predictive (anticipatory) or reactive (compensatory), or a combination of both. The former involve a voluntary movement or an increase in muscle activity to anticipate an expected disturbance, while the latter involve a muscular movement or response following an unexpected disturbance.
These strategies are applied either in static or semi-static situations or in dynamic situations (with or without displacement).
Standard balance tests (sway analysis protocols) have proved very useful in assessing and monitoring the level of control and the postural strategy adopted in a static or semi-static position over time. With Gyko, the performance of these tests can be measured, based on objective and comparable data, without affecting the subject’s capabilities.
With regard to the standard sway test, the most interesting parameters are (see Figure 1):
- Length of the ball of yarn, that is, of the overall displacement of the COM during the test. It indicates the energy consumed by the system: the greater the length, the greater the energy expenditure.
- Average length of the anteroposterior and medial-lateral oscillations, which makes it possible to understand whether the subject tends to move forward or backward, right or left.
- Surface of the ellipse, which contains 90% of the points of the ball. It represents the precision of the postural system, which is inversely proportional to the width of the area.
- The average speed of displacement is an index of fatigue: the higher its value, the greater the effort to maintain orthostatic posture.
- Frequency of the oscillations of the human body obtained via Fourier transform.
Restoring postural control is an integral and essential part of rehabilitation for a wide range of musculoskeletal and neurological disorders. The use of objective parameters for patient monitoring can make work easier for the health professionals who regularly perform assessments and treatments
 A. S. Pollock, B. R. Durward, P. J. Rowe, and J. P. Paul, “What is balance?,” Clin. Rehabil., vol. 14, no. 4, pp. 402–406, Aug. 2000, doi: 10.1191/0269215500cr342oa.