Balance is defined as keeping the centre of mass of a body within its support base . In humans, a properly functioning system of balance enables perceiving the movement of the body, identifying its orientation with respect to gravity, direction and speed and consequently carrying out more or less conscious postural adjustments in order to maintain stability. This complex control and adjustment mechanism takes place under various conditions and activities, whether static, semi-static or dynamic.
Postural stability is fundamental not only in everyday situations, but in almost all sports . Static balance, for example, is essential in archery. On the contrary, dynamic balance plays an important role in activities such as snowboarding, skateboarding, and windsurfing. In karate, tai-chi, yoga, ballet, and gymnastics, the goal is to control balance in different positions, which may vary in difficulty depending on the specialization. Precision in controlling the centre of mass (COM) is also fundamental in climbing, mountaineering, artistic skating and ice hockey where the area of support is greatly reduced.
In sports activity, impaired postural stability can lead to major compensations that can lead to the development of overloads and possible injuries to the weakest parts of the system (joints, tendons and muscles), which is why it is essential to measure and train the athlete’s capabilities.
To evaluate and monitor over time the level of control and the postural strategies implemented, bi- and mono-podalic balance tests (sway analysis protocols) are very useful. Gyko, enables measuring the performance of such tests, with objective and comparable values, without interfering with the subject's capabilities.
In the sway test, the most interesting parameters are (see Fig. 1):
- Length of the projection or of the total path of the COM during the test. It is an index of the energy spent by the system, the longer it is, the more energy is consumed.
- Average length of the antero-posterior and mid-lateral sways that permits understanding whether the subject tends to move forward or backward, right or left.
- Surface area of the ellipse that contains 90% of the points of the projection. It represents the precision of the postural system which is inversely proportional to the amplitude of the area.
- Mean displacement speed is a fatigue index: the higher its value, the greater the effort to maintain orthostatic posture
- Frequency of the sways of the human body obtained by Fourier transform.
Dynamic balance monitoring can instead be performed during activities that are the basis of the typical movements of every sport, such as running for example. In this case, OptoJump and Gyko provide useful parameters for identifying the possible source of a stability problem and the mechanism implemented for responding to such disturbance. The values reflect those measured in the sway tests (see fig. 2).
These parameters are useful for discriminating the presence of compensating movements of the upper limbs when running, such as the tendency to move the trunk in the mid-lateral or antero-posterior direction. In terms of dynamic posture, during marching in place, walking and running tests OptoJump enables measuring the asymmetry and the coefficient of variability (i.e. the cost necessary to maintain an economic and symmetrical action).
 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.
 “EBSCOhost | 78302564 | ASSESSMENT OF BALANCE IN SPORT: SCIENCE AND REALITY.” (accessed Apr. 20, 2020).