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We explored a variant of juggling in which human adults were asked to rhythmically bounce a soccer ball with their dominant foot while standing on the other foot. Eight subjects performed the task at three prescribed heights and one free height condition. Kinematic analyses of foot movement at ball-foot impact showed that, for the smallest height, foot acceleration was positive or zero at impact, which indicates an active stabilization regime. Increasing juggling height resulted in foot acceleration becoming increasingly negative at impact, which is required for a passive dynamical stability regime. These results show that skilled soccer jugglers exploit the passive stability regime afforded by the task, but that similar stability can be achieved with an active stabilization strategy.

The adiabatic transformability hypothesis for non-conservative, non-rate-limited biological systems put forward by Kugler and Turvey [Kugler PN, Turvey MT (1987) Information, natural law, and the self-assembly of rhythmic movements, Erlbaum, Hillsdale, NJ] is evaluated in a ball-bouncing task as a function of skill level. We hypothesized that, when a basketball player increases or decreases the frequency of his limb motion in a vertical ball-bouncing task, the transformation should be characterized as adiabatic. Confirmation of this hypothesis would lend support to the body of knowledge that suggests that physical-biological laws guide the behavior of people engaged in motor tasks, including their acquisition of skill. We videotaped and analyzed four participants – two intermediates and two experts – bouncing a ball from various heights, and measured the energy and kinematic relations of the ball and the participants' body segments. The task presents a challenge to certain predictions of the adiabatic hypothesis in evaluating changes in movement velocity (v) or frequency (f), and energy as adiabatic transformations. Among these are the constant relation between kinetic energy (Ek) per cycle and v, constancy of energy dissipated per cycle (Et) over changes in v and Ek, the ratio of Ek to Et per cycle (the “Q” values), and the relation of amplitude to v. From our observations, which are examined in regard to the insights of Kugler and Turvey about the relation of Ehrenfest's adiabatic theorem to biological systems, we confirm the basic adiabatic character of the task in analyzing both the ball alone and the relations of various body segments. In the segmental frame of reference, we found evidence of differences in energy-kinematic relations in the Q values between skill levels.

The adiabatic transformability hypothesis for non-conservative, non-rate-limited biological systems put forward by Kugler and Turvey [Kugler PN, Turvey MT (1987) Information, natural law, and the self-assembly of rhythmic movements, Erlbaum, Hillsdale, NJ] is evaluated in a ball-bouncing task as a function of skill level. We hypothesized that, when a basketball player increases or decreases the frequency of his limb motion in a vertical ball-bouncing task, the transformation should be characterized as adiabatic. Confirmation of this hypothesis would lend support to the body of knowledge that suggests that physical-biological laws guide the behavior of people engaged in motor tasks, including their acquisition of skill. We videotaped and analyzed four participants - two intermediates and two experts - bouncing a ball from various heights, and measured the energy and kinematic relations of the ball and the participants' body segments. The task presents a challenge to certain predictions of the adiabatic hypothesis in evaluating changes in movement velocity (v) or frequency (f), and energy as adiabatic transformations. Among these are the constant relation between kinetic energy (Ek) per cycle and v, constancy of energy dissipated per cycle (Et) over changes in v and Ek, the ratio of Ek to Et per cycle (the "Q" values), and the relation of amplitude to v. From our observations, which are examined in regard to the insights of Kugler and Turvey about the relation of Ehrenfest's adiabatic theorem to biological systems, we confirm the basic adiabatic character of the task in analyzing both the ball alone and the relations of various body segments. In the segmental frame of reference, we found evidence of differences in energy-kinematic relations in the Q values between skill levels.

Nous avons préparé par une méthode de Piper et Polich modifiée des mono cristaux cubiques de ZnSe de bonne qualité optique et qui présentent un effet électro-optique linéaire. L'étude expérimentale de cet effet a permis de constater que le coefficient électro-optique r41 du ZnSe varie avec la longueur d'onde (0,5 μ < λ < 0,6 μ), mais que par contre l'intensité de la modulation optique semble indépendante de λ et ne dépend que du champ électrique appliqué au cristal.