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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

Task effect on admittance of a typical subject. For each of the four repetitions, the magnitude (top panel) and phase (bottom panel) are shown for FT (dashed line), RT (solid line) and PT (dash–dotted line). The shown admittance is the response to a perturbation with a bandwidth of 0.7 Hz (supplemented with reduced power up to 40 Hz)
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Fig5: Task effect on admittance of a typical subject. For each of the four repetitions, the magnitude (top panel) and phase (bottom panel) are shown for FT (dashed line), RT (solid line) and PT (dash–dotted line). The shown admittance is the response to a perturbation with a bandwidth of 0.7 Hz (supplemented with reduced power up to 40 Hz)

Mentions: As hypothesized, the admittance was substantially influenced by task instruction. Figure 5 presents the admittance during four repetitions of one subject performing the three task instructions. The largest admittance occurs during FT (i.e., minimized force deviations), a smaller, but still large, admittance during RT (i.e., minimized muscle activity), and a small admittance during PT (i.e., minimized position deviations). These task-dependent changes in admittance were consistent over all subjects: a significantly (p < 0.01) higher admittance was found for FTs with respect to RTs up to 3.0 Hz, and a significantly (p < 0.01) lower admittance was found for PTs with respect to RTs up to 1.0 Hz. The (squared) coherence was high (not shown, >0.9 for all frequencies) indicating that the input–output behavior can be considered linear with low levels of noise.Fig. 5


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)

Task effect on admittance of a typical subject. For each of the four repetitions, the magnitude (top panel) and phase (bottom panel) are shown for FT (dashed line), RT (solid line) and PT (dash–dotted line). The shown admittance is the response to a perturbation with a bandwidth of 0.7 Hz (supplemented with reduced power up to 40 Hz)
© Copyright Policy
Related In: Results  -  Collection

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

Fig5: Task effect on admittance of a typical subject. For each of the four repetitions, the magnitude (top panel) and phase (bottom panel) are shown for FT (dashed line), RT (solid line) and PT (dash–dotted line). The shown admittance is the response to a perturbation with a bandwidth of 0.7 Hz (supplemented with reduced power up to 40 Hz)
Mentions: As hypothesized, the admittance was substantially influenced by task instruction. Figure 5 presents the admittance during four repetitions of one subject performing the three task instructions. The largest admittance occurs during FT (i.e., minimized force deviations), a smaller, but still large, admittance during RT (i.e., minimized muscle activity), and a small admittance during PT (i.e., minimized position deviations). These task-dependent changes in admittance were consistent over all subjects: a significantly (p < 0.01) higher admittance was found for FTs with respect to RTs up to 3.0 Hz, and a significantly (p < 0.01) lower admittance was found for PTs with respect to RTs up to 1.0 Hz. The (squared) coherence was high (not shown, >0.9 for all frequencies) indicating that the input–output behavior can be considered linear with low levels of noise.Fig. 5

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