Two Kinematic Synergies in Voluntary Whole-Body Movements During Standing

Abstract

Freitas, Sandra M.S.F., Marcos Duarte, and Mark L. Latash. Two kinematic synergies in voluntary whole-body movements during standing. J Neurophysiol 95: 636 -645, 2006. First published November 2, 2005 doi:10.1152/jn.00482.2005. We used a particular computational approach, the uncontrolled manifold hypothesis, to investigate joint angle covariation patterns during whole-body actions performed by standing persons. We hypothesized that two kinematic synergies accounted for the leg/trunk joint covariation across cycles during a rhythmic whole-body motion to stabilize two performance variables, the trunk orientation in the external space and the horizontal position of the center of mass (COM). Subjects stood on a force plate and performed whole-body rhythmic movements for 45 s under visual feedback on one of the four variables, the position of the center of pressure or the angle in one of the three joints (ankle, knee, or hip). The Fitts-like paradigm was used with two target amplitudes and six indices of difficulty (ID) for each of the four variables. This was done to explore the robustness of kinematic postural synergies. A speedaccuracy trade-off was observed in all feedback conditions such that the movement time scaled with ID and the scaling differed between the two movement amplitudes. Principal-component (PC) analysis showed the existence of a single PC in the joint space that accounted for over 95% of the joint angle variance. Analysis within the uncontrolled manifold hypothesis has shown that data distributions in the joint angle space were compatible with stabilization of both trunk orientation and COM location. We conclude that trunk orientation and the COM location are stabilized by co-varied changes of the major joint angles during whole-body movements. Despite the strong effects of movement amplitude and ID on performance, the structure of the joint variance showed only minor dependence on these task parameters. The two kinematic synergies (co-varied changes in the joint angles that stabilized the COM location and trunk orientation) have proven to be robust over a variety of tasks.

Control and Estimation of Posture During Quiet Stance Depends on Multijoint Coordination

“…A recent study by Freitas and colleagues used the UCM approach to study postural responses to voluntary shifts in the COP (Freitas et al 2006). Subjects achieved these shifts by oscillating either about the ankle, knee, or hip (which included trunk flexion-extension).…”

Hierarchies of synergies: an example of two-hand, multi-finger tasks

“…Examples include the coordination of articulators during speech (Abbs and Gracco 1984), of arms during loading and unloading (Dufosse et al 1985;Paulingnan et al 1989), of joints during pointing, reaching, standing-up, and swaying (Domkin et al 2002;Freitas et al 2006;Scholz and Schöner 1999;Wang and Stelmach 1998), of muscles during standing and stepping (Krishnamoorthy et al 2003;Wang et al 2005), and of digits during pressing, grasping, and holding an object (Gao et al 2005;Santello and Soechting 2000;Scholz and Latash 1998;Shim et al 2005). Very few studies, however, have addressed synergies at different levels of an involved control hierarchy.…”

Neurobiologically Inspired Distributed and Hierarchical System for Control and Learning

“…However, it would be highly likely that a coordinate at an area is selected to conveniently process control variables from high level command to low Level execution. For example, Freitas et al (2006) proposed that voluntary standing movements are maintained by stabilization of two control variables, trunk orientation and center of mass location. The control variables could be directly sensed or estimated via neural processing.…”