Résumé
INTRODUCTION. This presentation will emphasize the nonlinear nature of coordination dynamics underlying skilled performance in the motor domain. One particular aspect which receives increasing attention in sports research is 1/f scaling (or ‘pink noise’), present in the intra-individual variability of human behavior. This ‘background noise’ expresses the extent to which behavior is resulting from interdependence across many general-purpose processes, rather than from a few task-specific components. Research examples will include the performance of rhythmical aiming movements in the classical Fitts task. Evidence is provided that movement variability is not random, but shows 1/f scaling, which appears more clearly after practice. Moreover, speed-accuracy trade-off analyzed at three different levels of observation revealed nested scales of performance. The main empirical study that will be discussed addresses rowing performance, in which continuous coordination is crucial. We particularly focused on the temporal structure in rowing strokes, and whether this is characterized by 1/f scaling. Furthermore, we compared the movement variability in performance of high-level rowers with that of medium-level rowers.METHODS. Four high-level and 5 medium-level rowers performed 550 strokes on a rowing ergometer. A force sensor registered the exerted force time series at 100 Hz, from which we calculated the force peaks for each stroke. Detrended Fluctuation Analysis (DFA) was used to quantify the temporal structure of the resulting time series of peak-to-peak durations.RESULTS. DFA revealed that the noise pattern of the peak-to-peak duration time series differed significantly from random variation for each rower. In addition, movement variability was closer to pink noise for all high-level rowers than for all medium-level rowers, making a sharp cut between the two groups.DISCUSSION. This result is one of the first real demonstrations in sport performance of pink noise, the hallmark of well-coordinated and effective complex systems behavior. The relation between skill level and noise pattern emphasizes that temporal variability provides crucial information about the quality of coordinated movements , and should not be discarded in sports research.