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A rigorous model of reflex function indicates that position and force feedback are flexibly tuned to position and force tasks.

Mugge W, Abbink DA, Schouten AC, Dewald JP, van der Helm FC - Exp Brain Res (2009)

Bottom Line: This study aims to quantify the separate contributions of muscle force feedback, muscle spindle activity and co-contraction to the performance of voluntary tasks ("reduce the influence of perturbations on maintained force or position").Inhibitory, as well as excitatory force feedback, was needed to account for the full range of measured experimental behaviors.In conclusion, force feedback plays an important role in the studied motion control tasks (excitatory during position tasks and inhibitory during force tasks), implying that spindle-mediated feedback is not the only significant adaptive system that contributes to the maintenance of posture or force.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Neuromuscular Control, Department of Biomechanical Engineering, Mechanical Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. w.mugge@tudelft.nl

ABSTRACT
This study aims to quantify the separate contributions of muscle force feedback, muscle spindle activity and co-contraction to the performance of voluntary tasks ("reduce the influence of perturbations on maintained force or position"). Most human motion control studies either isolate only one contributor, or assume that relevant reflexive feedback pathways during voluntary disturbance rejection tasks originate mainly from the muscle spindle. Human ankle-control experiments were performed, using three task instructions and three perturbation characteristics to evoke a wide range of responses to force perturbations. During position tasks, subjects (n = 10) resisted the perturbations, becoming more stiff than when being relaxed (i.e., the relax task). During force tasks, subjects were instructed to minimize force changes and actively gave way to imposed forces, thus becoming more compliant than during relax tasks. Subsequently, linear physiological models were fitted to the experimental data. Inhibitory, as well as excitatory force feedback, was needed to account for the full range of measured experimental behaviors. In conclusion, force feedback plays an important role in the studied motion control tasks (excitatory during position tasks and inhibitory during force tasks), implying that spindle-mediated feedback is not the only significant adaptive system that contributes to the maintenance of posture or force.

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Related in: MedlinePlus

Model fits using incorrect neuromusculoskeletal model structures. Magnitude and phase of the parameterized models (solid lines) are shown on top of the frequency response functions from the ARMAX-approximated signals (averaged over four repetitions, represented by dotted lines). As a reference, the spectral frequency response functions estimated from the measured signals (averaged over four repetitions) are shown by dashed lines. The behavior was measured in response to the 0.7 Hz perturbation bandwidth. Left: fit results of a model without GTO muscle force feedback on data of a typical subject performing a PT. Right: fit results of a model with long-latency instead of short-latency reflexes on data of a typical subject performing an FT
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Fig9: Model fits using incorrect neuromusculoskeletal model structures. Magnitude and phase of the parameterized models (solid lines) are shown on top of the frequency response functions from the ARMAX-approximated signals (averaged over four repetitions, represented by dotted lines). As a reference, the spectral frequency response functions estimated from the measured signals (averaged over four repetitions) are shown by dashed lines. The behavior was measured in response to the 0.7 Hz perturbation bandwidth. Left: fit results of a model without GTO muscle force feedback on data of a typical subject performing a PT. Right: fit results of a model with long-latency instead of short-latency reflexes on data of a typical subject performing an FT

Mentions: The model results section shows that the model that included inhibitory as well as excitatory MS and GTO yields accurate fits for all conditions. This may be surprising, given the prevailing neurophysiologic view of GTO being essentially inhibitory and MS excitatory. Could a model with only MS yield the same fits? The solid line in the left panel of Fig. 9 shows the results of a typical parameter fit for PT, using a model comprising all parameters except the GTO force feedback gain kf. The reduced model could not accurately capture the dynamics of the admittance during FT and PT, resulting in bad fits, substantially reduced VAFs and unrealistic parameter values. Could a model with only inhibitory GTO yield accurate fits? The implementation of strictly inhibitory GTO muscle force feedback did result in accurate fits for FT; however, the behavior during PT can only be accurately described with a model that incorporates excitatory muscle force feedback.Fig. 9


A rigorous model of reflex function indicates that position and force feedback are flexibly tuned to position and force tasks.

Mugge W, Abbink DA, Schouten AC, Dewald JP, van der Helm FC - Exp Brain Res (2009)

Model fits using incorrect neuromusculoskeletal model structures. Magnitude and phase of the parameterized models (solid lines) are shown on top of the frequency response functions from the ARMAX-approximated signals (averaged over four repetitions, represented by dotted lines). As a reference, the spectral frequency response functions estimated from the measured signals (averaged over four repetitions) are shown by dashed lines. The behavior was measured in response to the 0.7 Hz perturbation bandwidth. Left: fit results of a model without GTO muscle force feedback on data of a typical subject performing a PT. Right: fit results of a model with long-latency instead of short-latency reflexes on data of a typical subject performing an FT
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2821582&req=5

Fig9: Model fits using incorrect neuromusculoskeletal model structures. Magnitude and phase of the parameterized models (solid lines) are shown on top of the frequency response functions from the ARMAX-approximated signals (averaged over four repetitions, represented by dotted lines). As a reference, the spectral frequency response functions estimated from the measured signals (averaged over four repetitions) are shown by dashed lines. The behavior was measured in response to the 0.7 Hz perturbation bandwidth. Left: fit results of a model without GTO muscle force feedback on data of a typical subject performing a PT. Right: fit results of a model with long-latency instead of short-latency reflexes on data of a typical subject performing an FT
Mentions: The model results section shows that the model that included inhibitory as well as excitatory MS and GTO yields accurate fits for all conditions. This may be surprising, given the prevailing neurophysiologic view of GTO being essentially inhibitory and MS excitatory. Could a model with only MS yield the same fits? The solid line in the left panel of Fig. 9 shows the results of a typical parameter fit for PT, using a model comprising all parameters except the GTO force feedback gain kf. The reduced model could not accurately capture the dynamics of the admittance during FT and PT, resulting in bad fits, substantially reduced VAFs and unrealistic parameter values. Could a model with only inhibitory GTO yield accurate fits? The implementation of strictly inhibitory GTO muscle force feedback did result in accurate fits for FT; however, the behavior during PT can only be accurately described with a model that incorporates excitatory muscle force feedback.Fig. 9

Bottom Line: This study aims to quantify the separate contributions of muscle force feedback, muscle spindle activity and co-contraction to the performance of voluntary tasks ("reduce the influence of perturbations on maintained force or position").Inhibitory, as well as excitatory force feedback, was needed to account for the full range of measured experimental behaviors.In conclusion, force feedback plays an important role in the studied motion control tasks (excitatory during position tasks and inhibitory during force tasks), implying that spindle-mediated feedback is not the only significant adaptive system that contributes to the maintenance of posture or force.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Neuromuscular Control, Department of Biomechanical Engineering, Mechanical Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. w.mugge@tudelft.nl

ABSTRACT
This study aims to quantify the separate contributions of muscle force feedback, muscle spindle activity and co-contraction to the performance of voluntary tasks ("reduce the influence of perturbations on maintained force or position"). Most human motion control studies either isolate only one contributor, or assume that relevant reflexive feedback pathways during voluntary disturbance rejection tasks originate mainly from the muscle spindle. Human ankle-control experiments were performed, using three task instructions and three perturbation characteristics to evoke a wide range of responses to force perturbations. During position tasks, subjects (n = 10) resisted the perturbations, becoming more stiff than when being relaxed (i.e., the relax task). During force tasks, subjects were instructed to minimize force changes and actively gave way to imposed forces, thus becoming more compliant than during relax tasks. Subsequently, linear physiological models were fitted to the experimental data. Inhibitory, as well as excitatory force feedback, was needed to account for the full range of measured experimental behaviors. In conclusion, force feedback plays an important role in the studied motion control tasks (excitatory during position tasks and inhibitory during force tasks), implying that spindle-mediated feedback is not the only significant adaptive system that contributes to the maintenance of posture or force.

Show MeSH
Related in: MedlinePlus