Einleitung

The constraints-led perspective suggests three factors that form a basis for understanding complex phenomena in the training process. We will examine these in the context of three subsystems: the performer, the task and the environment. These three factors can provide basic variables for complex motor control and motor learning theories and can be used by coaches to improve performance by manipulating them during practice. However, we should always keep in mind that models for certain phenomena are simplified projections of reality (Stachowiak, 1973). In many cases the elements that were excluded during modeling are also neglected in the application phase. Therefore models can produce a new reality that is different from the original one. Specific problems that: occur because of a separation of the performer and the environment can be seen in biomechanics and the psychology of perception, for example. In biomechanics, typically three types of forces that are assumed to cause movement are analyzed. While muscular and gravitational forces can clearly be assigned to either the performer or the environment, inertial forces can hardly be assigned to either. This seems to be even more important when we take into consideration the constant changes of the inertial tensors of all limbs in living systems that are caused by blood flow and breathing. These constant changes take care of involuntary variations in so-called movement repetitions, even if not intended by the performer. With respect to psychology of perception, the separation of performer and environment leads to similar problems. Depending on one's philosophy, the perception process is considered differently: (1) as a simple projection of the environment into the perception apparatus of the performer, allowing a clear separation of performer and environment; (2) as an active process of the performer that selects information from the environment based on his/her past experience; or (3) as dependent on the performer's activities not allowing a separation of the performer and the environment. Similar to the involuntary biomechanical changes of the inertial tensor, the perception process is also changing implicitly all the time due to the influence of previous perception processes. These changes of the performer and the environment and their interactions over time seem to be an essential characteristic of motor control and motor learning, especially in sports, and have been widely neglected in traditional models. Einleitung