Relativistic effects in single-joint voluntary movements.

We assume that there is an upper limit for the rate of change of controlled variables in the motor control system. Superposition of two single-joint motor programs can lead to a distortion of their simple algebraic summation similar to relativistic Lorenz transformations. Experiments were carried out with the subjects performing fast oscillatory elbow movements on the background of a smooth elbow flexion. Changes in the period of oscillations during the smooth movement were used as index of time transformations. Statistically 5%-7% changes in the period were observed for each of the subjects corresponding to the predictions of the model.