A simple method was designed to evaluate visual abilities such as disance visual acuity, binocular horizontal visual field, simple and choice visual reaction times, and stereoscopic vision in skilled 11- to 13-yr.-old basketball players participating in a 15-day summer training camp. On a test battery, visual abilities were monitored in 473 players of the Spanish Basketball Federation over a 5-yr. period. The players showed outstanding scores on distance visual acuity and stereoscopic vision, and good visual reaction times and horizontal visual fields. When scores were compared by sex and age, significant differences on certain visual measures were observed. Many layers showed crossed eye-hand dominance. Visual screening programs may help promote visual health among junior basketball players and could be used for performance training.

We present a method of modeling the basin of attraction as a three-dimensional function describing a two-dimensional manifold on which the dynamics of the system evolves from experimental time series data. Our method is based on the density of the data set and uses numerical optimization and data modeling tools. We also show how to obtain analytic curves that describe both the contours and the boundary of the basin. Our method is applied to the problem of regaining balance after perturbation from quiet vertical stance using data of an elite athlete. Our method goes beyond the statistical description of the experimental data, providing a function that describes the shape of the basin of attraction. To test its robustness, our method has also been applied to two different data sets of a second subject and no significant differences were found between the contours of the calculated basin of attraction for the different data sets. The proposed method has many uses in a wide variety of areas, not just human balance for which there are many applications in medicine, rehabilitation, and sport.

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We show how asymmetries in the movement patterns during the process of regaining balance after perturbation from quiet stance can be modeled by a set of coupled vector fields for the derivative with respect to time of the angles between the resultant ground reaction forces and the vertical in the anteroposterior and mediolateral directions. In our model, which is an adaption of the model of Stirling and Zakynthinaki (2004), the critical curve, defining the set of maximum angles one can lean to and still correct to regain balance, can be rotated and skewed so as to model the effects of a repetitive training of a rotational movement pattern. For the purposes of our study a rotation and a skew matrix is applied to the critical curve of the model. We present here a linear stability analysis of the modified model, as well as a fit of the model to experimental data of two characteristic "asymmetric" elite athletes and to a "symmetric" elite athlete for comparison. The new adapted model has many uses not just in sport but also in rehabilitation, as many work place injuries are caused by excessive repetition of unaligned and rotational movement patterns.Human balance is a topic of much current interest ~ in which tools for nonlinear dynamics have been found to be very useful in helping to understand its complex behavior. ~ ' ~ Many jobs, professions, or sports involve such conditions in which numerous movement patterns are repeated daily for many years. As a result the human body adapts in such a way that it becomes very skillful at doing this particular movement often at the expense of more natural movements. This adaption often leads to injuries, postural imbalances (i.e., where the axis of the body remains permanently skewed), and the situation where the balance of an individual is no longer symmetric (i.e., it is rotated), and hence they have a dominant side. We show here how the model of the process of regaining balance presented in Ref. 7 can be modified to account for the case where the balance of an individual has been rotated and skewed as an adaption to numerous repetitions over many years of very similar movement patterns. Our aim is to present a model that, from a small number of experimentally recorded parameters, can provide important details regarding the asymmetries in the movement patterns of an individual. The research presented here can also be applied to cases of balance asymmetries arising as a result of injury or disease.

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