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Stability of Phase Relationships While Coordinating Arm Reaches with Whole Body Motion.

Bakker RS, Selen LP, Medendorp WP - PLoS ONE (2015)

Bottom Line: For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship.For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships.Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns.

View Article: PubMed Central - PubMed

Affiliation: Radboud University Nijmegen, Donders Centre for Cognition, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.

ABSTRACT
The human movement repertoire is characterized by the smooth coordination of several body parts, including arm movements and whole body motion. The neural control of this coordination is quite complex because the various body parts have their own kinematic and dynamic properties. Behavioral inferences about the neural solution to the coordination problem could be obtained by examining the emerging phase relationship and its stability. Here, we studied the phase relationships that characterize the coordination of arm-reaching movements with passively-induced whole-body motion. Participants were laterally translated using a vestibular chair that oscillated at a fixed frequency of 0.83 Hz. They were instructed to reach between two targets that were aligned either parallel or orthogonal to the whole body motion. During the first cycles of body motion, a metronome entrained either an in-phase or an anti-phase relationship between hand and body motion, which was released at later cycles to test phase stability. Results suggest that inertial forces play an important role when coordinating reaches with cyclic whole-body motion. For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship. When the latter was imposed, it readily transitioned or drifted back toward an in-phase relationship at cycles without metronomic entrainment. For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships. Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns. We discuss how predictive control and impedance control processes could be considered important mechanisms underlying the rhythmic coordination of arm reaches and body motion.

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The 2-link model and predictions.Diagram of the 2-link arm model (B) Costs based on the minimum energy model. Cost is expressed as the inverse of the summed joint torques for the different phase angles between hand and whole body motion (left); Costs based on the minimum end-point model. Cost is expressed in terms of end-point variance for the different phase angles between hand and whole body motion (right).
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pone.0146231.g002: The 2-link model and predictions.Diagram of the 2-link arm model (B) Costs based on the minimum energy model. Cost is expressed as the inverse of the summed joint torques for the different phase angles between hand and whole body motion (left); Costs based on the minimum end-point model. Cost is expressed in terms of end-point variance for the different phase angles between hand and whole body motion (right).

Mentions: We investigated whether biomechanical cost factors, either energy expenditure or endpoint accuracy, underlie the coordination patterns between arm movements and whole body motion. If the coordination were driven by energetic costs, we would expect subjects to show a more stable phase relationship around the minimum energy solution. If arm-trunk coordination were driven by the minimization of endpoint variance, we would expect subjects to show more stability for the phase relationship minimizing endpoint variance. To make predictions about the phase relationships, we built a generic planar arm model (Fig 2A), by which reaching under whole body motion was simulated. The simulation provided estimates of the energetic costs and the endpoint variance associated with the different phase relationships between arm and whole body motion. From the estimates, we derived the ‘optimal’ phase relationship.


Stability of Phase Relationships While Coordinating Arm Reaches with Whole Body Motion.

Bakker RS, Selen LP, Medendorp WP - PLoS ONE (2015)

The 2-link model and predictions.Diagram of the 2-link arm model (B) Costs based on the minimum energy model. Cost is expressed as the inverse of the summed joint torques for the different phase angles between hand and whole body motion (left); Costs based on the minimum end-point model. Cost is expressed in terms of end-point variance for the different phase angles between hand and whole body motion (right).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4697800&req=5

pone.0146231.g002: The 2-link model and predictions.Diagram of the 2-link arm model (B) Costs based on the minimum energy model. Cost is expressed as the inverse of the summed joint torques for the different phase angles between hand and whole body motion (left); Costs based on the minimum end-point model. Cost is expressed in terms of end-point variance for the different phase angles between hand and whole body motion (right).
Mentions: We investigated whether biomechanical cost factors, either energy expenditure or endpoint accuracy, underlie the coordination patterns between arm movements and whole body motion. If the coordination were driven by energetic costs, we would expect subjects to show a more stable phase relationship around the minimum energy solution. If arm-trunk coordination were driven by the minimization of endpoint variance, we would expect subjects to show more stability for the phase relationship minimizing endpoint variance. To make predictions about the phase relationships, we built a generic planar arm model (Fig 2A), by which reaching under whole body motion was simulated. The simulation provided estimates of the energetic costs and the endpoint variance associated with the different phase relationships between arm and whole body motion. From the estimates, we derived the ‘optimal’ phase relationship.

Bottom Line: For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship.For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships.Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns.

View Article: PubMed Central - PubMed

Affiliation: Radboud University Nijmegen, Donders Centre for Cognition, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.

ABSTRACT
The human movement repertoire is characterized by the smooth coordination of several body parts, including arm movements and whole body motion. The neural control of this coordination is quite complex because the various body parts have their own kinematic and dynamic properties. Behavioral inferences about the neural solution to the coordination problem could be obtained by examining the emerging phase relationship and its stability. Here, we studied the phase relationships that characterize the coordination of arm-reaching movements with passively-induced whole-body motion. Participants were laterally translated using a vestibular chair that oscillated at a fixed frequency of 0.83 Hz. They were instructed to reach between two targets that were aligned either parallel or orthogonal to the whole body motion. During the first cycles of body motion, a metronome entrained either an in-phase or an anti-phase relationship between hand and body motion, which was released at later cycles to test phase stability. Results suggest that inertial forces play an important role when coordinating reaches with cyclic whole-body motion. For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship. When the latter was imposed, it readily transitioned or drifted back toward an in-phase relationship at cycles without metronomic entrainment. For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships. Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns. We discuss how predictive control and impedance control processes could be considered important mechanisms underlying the rhythmic coordination of arm reaches and body motion.

Show MeSH
Related in: MedlinePlus