A new approach to quantify asymmetry in human movement.

In this perspective paper, we propose a new approach to quantify the asymmetries in human movement. Before describing this approach, we delve into the asymmetry in human movement, often defined as the opposite of symmetry, and its implications for studying human movement. We critically examine the various methods available to quantify and describe bilateral differences, from arbitrary thresholds (such as the commonly employed 10-15% difference) to the measure of the smallest meaningful changes, and we stress the need for consideration of interindividual variability in the analysis. Our proposal centers on a straightforward metric, the probability of agreement, and a corresponding plot summarizing the agreement between measures from two limbs. Critically, the agreement between two limbs depends on the value of the clinically acceptable difference. The agreement will increase with larger values of clinically acceptable difference and decrease with smaller values of clinically acceptable difference. Data from various movements and conditions in athletes' sports training and rehabilitation are used to illustrate this approach. Our perspective provides valuable insights into the nature of asymmetry in human movement, considering that a rational understanding of asymmetry in human movement requires a thoughtful approach encompassing both statistical and clinical significance. The data and codes employed in our research are openly accessible in the supplementary materials, enabling others in the field to replicate and build upon our findings.