Angular momentum synergies during walking

Université Lyon 1, Villeurbanne, France.
Experimental Brain Research (Impact Factor: 2.04). 09/2009; 197(2):185-97. DOI: 10.1007/s00221-009-1904-4
Source: PubMed


We studied the coordination of body segments during treadmill walking. Specifically, we used the uncontrolled manifold hypothesis framework to quantify the segmental angular momenta (SAM) synergies that stabilize (i.e., reduce the across trials variability) the whole body angular momentum (WBAM). Seven male subjects were asked to walk over a treadmill at their comfortable walking speed. A 17-segment model, fitted to the subject's anthropometry, was used to reconstruct their kinematics and to compute the SAM and WBAM in three dimensions. A principal component analysis was used to represent the 17 SAM by the magnitudes of the first five principal components. An index of synergy (DeltaV) was used to quantify the co-variations of these principal components with respect to their effect on the WBAM. Positive values of DeltaV were observed in the sagittal plane during the swing phase. They reflected the synergies among the SAM that stabilized (i.e., made reproducible from stride to stride) the WBAM. Negative values of DeltaV were observed in both frontal and sagittal plane during the double support phase. They were interpreted as "anti-synergies", i.e., a particular organization of the SAM used to adjust the WBAM. Based on these results, we demonstrated that the WBAM is a variable whose value is regulated by the CNS during walking activities, and that the nature of the WBAM control changed between swing phase and double support phase. These results can be linked with humanoid gait controls presently employed in robotics.

Download full-text


Available from: Bradford C Bennett, Jan 23, 2014
  • Source
    • "These ideas are implemented experimentally by computing ratios of the normalized variances orthogonal to and along a candidate manifold (Latash et al., 2002; Schöner & Scholz, 2007): if a larger variance is found along the candidate manifold than normal to it, the manifold is deemed to be a UCM, indicating that it is being used to organize motor control. This approach has been applied experimentally to many different tasks, including reaching (Freitas & Scholz, 2009), throwing (Yang & Scholz, 2005), sit-to-stand (Reisman et al., 2002), quiet standing (Hsu et al., 2007), hopping (Yen & Chang, 2010), and walking (Robert et al., 2009). The approach has also been used to explore how variance evolves over time during learning (Yang et al., 2007; Yang & Scholz, 2005). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Fluctuations in the repeated performance of human movements have been the subject of intense scrutiny because they are generally believed to contain important information about the function and health of the neuromotor system. A variety of approaches has been brought to bear to study these fluctuations. However it is frequently difficult to understand how to synthesize different perspectives to give a coherent picture. Here, we describe a conceptual framework for the experimental study of motor variability that helps to unify geometrical methods, which focus on the role of motor redundancy, with dynamical methods that characterize the error-correcting processes regulating the performance of skilled tasks. We describe how goal functions, which mathematically specify the task strategy being employed, together with ideas from the control of redundant systems, allow one to formulate simple, experimentally testable dynamical models of inter-trial fluctuations. After reviewing the basic theory, we present a list of five general hypotheses on the structure of fluctuations that can be expected in repeated trials of goal-directed tasks. We review recent experimental applications of this general approach, and show how it can be used to precisely characterize the error-correcting control used by human subjects.
    Full-text · Article · Nov 2013 · Human movement science
  • Source
    • "Strongly positive values of ΔV indicate that there is more variance within the UCM than orthogonal to it, i.e. one can claim that there is a synergy among the EV stabilizing the PV. Negative values of the index of synergy, less classically discussed, are more complex to handle (see [12] "
    [Show abstract] [Hide abstract]
    ABSTRACT: The importance of the organization of angular momenta during walking has been suggested by the efforts of researchers to use it to control and stabilize walking robots. However, there has been little attention to the use of angular momenta as a metric of human walking or to gain insights into the control of walking. This paper analyzes the angular momenta of the whole body (WBAM) and body segments of during walking. The normalized angular momenta about the body center of mass (CoM) of the body segments were computed about all three coordinate axes. The normalized angular momenta were small (
    Full-text · Conference Paper · Sep 2011
  • Source
    • "During normal walking, angular momentum is generated about the body's center-of-mass by movements of the body segments and the interaction of the feet with the ground that generates an external moment on the body. Previous studies have suggested that angular momentum is highly regulated by the central nervous system during walking (Herr and Popovic, 2008; Popovic et al., 2004a) and that control synergies or primitives may be used to provide this regulation (Popovic et al., 2004b; Robert et al., 2009). Others have suggested that controlling angular momentum may be important in maintaining dynamic balance and preventing falls during walking (Simoneau and Krebs, 2000), sit-to-stand tasks (Reisman et al., 2002; Riley et al., 1997), and recovering from a trip (Pijnappels et al., 2004). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Walking is a complex dynamic task that requires the regulation of whole-body angular momentum to maintain dynamic balance while performing walking subtasks such as propelling the body forward and accelerating the leg into swing. In human walking, the primary mechanism to regulate angular momentum is muscle force generation. Muscles accelerate body segments and generate ground reaction forces that alter angular momentum about the body's center-of-mass to restore and maintain dynamic stability. In addition, gravity contributes to whole-body angular momentum through its contribution to the ground reaction forces. The purpose of this study was to generate a muscle-actuated forward dynamics simulation of normal walking to quantify how individual muscles and gravity contribute to whole-body angular momentum in the sagittal plane. In early stance, the uniarticular hip and knee extensors (GMAX and VAS), biarticular hamstrings (HAM) and ankle dorsiflexors (TA) generated backward angular momentum while the ankle plantar flexors (SOL and GAS) generated forward momentum. In late stance, SOL and GAS were the primary contributors and generated angular momentum in opposite directions. SOL generated primarily forward angular momentum while GAS generated backward angular momentum. The difference between muscles was due to their relative contributions to the horizontal and vertical ground reaction forces. Gravity contributed to the body's angular momentum in early stance and to a lesser extent in late stance, which was counteracted primarily by the plantar flexors. These results may provide insight into balance and movement disorders and provide a basis for developing locomotor therapies that target specific muscle groups.
    Full-text · Article · Jan 2011 · Journal of Biomechanics
Show more