Learning to tune the antero‑posterior propulsive forces during walking: a necessary skill for mastering upright locomotion in toddlers

This study examines the process of learning to walk from a functional perspective. To move forward, one must generate and control propulsive forces. To achieve this, it is necessary to create and tune a distance between the centre of mass (CoM) and the centre of pressure (CoP) along the antero-posterior axis. We hypothesize that learning to walk consists of learning how to calibrate these self-generated propulsive forces to control such distance.
We investigated this question with six infants (three girls and three boys) who we followed up weekly for the first 8 weeks after the onset of walking and then biweekly until they reached 14–16 weeks of walking experience. The infants’ walking patterns (kinematics and propelling forces) were captured via synched motion analysis and force plate.
The results show that the distance between the CoM and the CoP along the antero-posterior axis increased rapidly during the first months of learning to walk and that this increase was correlated with an increase in velocity. The initial small values of (CoM–CoP) observed at walking onset, coupled with small velocity are interpreted as the solution infants adopted to satisfy a compromise between the need to generate propulsive forces to move forward while simultaneously controlling the disequilibrium resulting
from creating a with distance between the CoM and CoP.

Blandine Bril, Lucile Dupuy, Gilles Dietrich, Daniela Corbetta

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Interpersonal Distance Modeling During Fighting Activities

The aim of this article is to elaborate a general framework for modeling dual
opposition activities, or more generally, dual interaction. The main hypothesis is that opposition behavior can be measured directly from a global variable and that the relative distance between the two subjects can be this parameter. Moreover, this parameter should be considered as multidimensional parameter depending not only on the dynamics of the subjects but also on the “internal” parameters of the subjects, such as sociological and/or emotional states. Standard and simple mechanical formalization will be used to model this multifactorial distance. To
illustrate such a general modeling methodology, this model was compared with actual data from an opposition activity like Japanese fencing (kendo). This model captures not only coupled coordination, but more generally interaction in two-subject activities.

Gilles Dietrich, Jonathan Bredin, and Yves Kerlirzin

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