THE ORGANIZATION OF MULTISEGMENTAL PULLS MADE BY STANDING HUMANS .1. NEAR-MAXIMAL PULLS

Complex multisegmental movements occur when standing subjects exert fo rceful, impulse-like pulls on a bimanually held handle. The degrees of freedom of this task were analyzed to provide a principled basis for understanding the act's coordination. Body posture was found to be des cribable by only two degrees of freedom, expressible as the anterior-p osterior and vertical coordinates of the center of mass (CM(AP), CM(V) ). Kinetic analysis revealed that the two major contributors to pullin g force depended only upon CM(AP) motion and the location of the cente r of pressure. Kinematic and kinetic data from six well-practiced subj ects pulling near their maxima were used to test the prediction of les s intersubject variability in CM(AP) than in CM(V). CM(AP) motions wer e qualitatively invariant, but CM(V) variation led to different moveme nt patterns among subjects. A dynamic model of CM(AP) motion was devel oped, and manipulation of its three degrees of freedom yielded CM(AP) trajectories that matched the empirical trajectories. It is suggested that the pull might be controlled with reference to these three parame ters.