The superposition principle applied to grasping an object producing moments outside anatomically-defined axes

Robertson, Jason W.; Johnston, Jamie A.

doi:10.1016/j.jbiomech.2012.04.020

Cited by 4 publications

(3 citation statements)

References 22 publications

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“…They found that the overall control inputs were designed using linear superposition, and the net results were generated based on two or more independent phenomena. Further, it has been reported that the principle of superposition is valid in the human hand grasp task, demonstrating the decoupled organization for grasp and rotational equilibrium Robertson & Johnston, 2012;Shim et al, 2005;Zatsiorsky et al, 2004). Specifically, fine-tuning the moment of normal forces or tangential forces significantly correlated with tuning at the point of force application (i.e., moment arm) rather than tuning of the normal force itself (Shim et al, 2003;Song et al, 2021;Zatsiorsky et al, 2004), which agrees with the findings of the present study.…”

Section: Discussionsupporting

confidence: 92%

Decoupled Control of Grasp and Rotation Constraints During Prehension of Weightless Objects

Park

Lee

et al. 2023

Motor Control

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Gravity provides critical information for the adjustment of body movement or manipulation of the handheld object. Indeed, the changes in gravity modify the mechanical constraints of prehensile actions, which may be accompanied by the changes in control strategies. The current study examined the effect of the gravitational force of a handheld object on the control strategies for subactions of multidigit prehension. A total of eight subjects performed prehensile tasks while grasping and lifting the handle by about 250 mm along the vertical direction. The experiment consisted of two conditions: lifting gravity-induced (1g) and weightless (0g) handheld objects. The weightless object condition was implemented utilizing a robot arm that produced a constant antigravitational force of the handle. The current analysis was limited to the two-dimensional grasping plane, and the notion of the virtual finger was employed to formulate the cause–effect chain of elemental variables during the prehensile action. The results of correlation analyses confirmed that decoupled organization of two subsets of mechanical variables was observed in both 1g and 0g conditions. While lifting the handle, the two subsets of variables were assumed to contribute to the grasping and rotational equilibrium, respectively. Notably, the normal forces of the thumb and virtual finger had strong positive correlations. In contrast, the normal forces had no significant relationship with the variables as to the moment of force. We conclude that the gravitational force had no detrimental effect on adjustments of the mechanical variables for the rotational action and its decoupling from the grasping equilibrium.

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Section: Discussionsupporting

confidence: 92%

Decoupled Control of Grasp and Rotation Constraints During Prehension of Weightless Objects

Park

Lee

et al. 2023

Motor Control

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“…Concerning the presence of interaction effects at higher movement frequencies, some of these effects (GF magnification) may not directly stem from the superposition of voluntary and automatic GF control, however their precise origin remain to be found and future studies will have to investigate whether these effects persist with more extended practice. At a more general level, this study further documents the superposition principle in human grasp control [50] , , a concept suggesting that grasping can be divided into multiple, and independently controlled components that summate to form a complete command [52] . Finally, despite restrictions with respect to temporal constraints, this study extends the ability of the nervous system to flexibly combine automatic and voluntary control beyond basic functions such as breathing, swallowing, and walking [1] , [2] , [5] , [7] , [8] .…”

Section: Discussionmentioning

confidence: 53%

Superposition of Automatic and Voluntary Aspects of Grip Force Control in Humans during Object Manipulation

Danion

2013

PLoS ONE

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When moving grasped objects, people automatically modulate grip force (GF) with movement-dependent load force (LF) in order to prevent object slip. However, GF can also be modulated voluntarily as when squeezing an object. Here we investigated possible interactions between automatic and voluntary GF control. Participants were asked to generate horizontal cyclic movements (between 0.6 and 2.0 Hz) of a hand-held object that was restrained by an elastic band such that the load force (LF) reached a peak once per movement cycle, and to simultaneously squeeze the object at each movement reversal (i.e., twice per cycle). Participants also performed two control tasks in which they either only moved (between 0.6 and 2.0 Hz) or squeezed (between 1.2 and 4.0 Hz) the object. The extent to which GF modulation in the simultaneous task could be predicted from the two control tasks was assessed using power spectral analyses. At all frequencies, the GF power spectra from the simultaneous task exhibited two prominent components that occurred at the cycle frequency (ƒ) and at twice this frequency (2ƒ), whereas the spectra from the movement and squeeze control task exhibited only single peaks at ƒ and 2ƒ, respectively. At lower frequencies, the magnitudes of both frequency components in the simultaneous task were similar to the magnitudes of the corresponding components in the control tasks. However, as frequency increased, the magnitudes of both components in the simultaneous task were greater than the magnitudes of the corresponding control task components. Moreover, the phase relationship between the ƒ components of GF and LF began to drift from the value observed in the movement control task. Overall these results suggest that, at lower movement frequencies, voluntary and automatic GF control processes operate at different hierarchical levels. Several mechanisms are discussed to account for interaction effects observed at higher movement frequencies.

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“…The principle has been shown to hold in a variety of experimental conditions (Ambike, Paclet, Latash, & Zatsiorsky, 2013; Niu, Latash, & Zatsiorsky, 2012; Robertson & Johnston, 2012; Shim, Latash, & Zatsiorsky, 2005b). In a recently published paper (Singh, Zatsiorsky, & Latash, 2013) we showed that adaptations to fatigue of a single digit violate the principle of superposition.…”

Section: Introductionmentioning

confidence: 98%

Prehension Synergies During Fatigue of a Single Digit: Adaptations in Control With Referent Configurations

Singh¹,

Zatsiorsky²,

Latash³

2014

Motor Control

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The purpose of the current study was to investigate the effects of exercise-induced fatigue of a digit on prehension synergies in a static precision grasp. One group of participants performed the fatiguing exercise using the thumb (group-thumb) and the second group performed the exercise using the index finger (group-index). Our first hypothesis was that fatigue would trigger changes in the co-variation of forces and moments of force that violate the principle of superposition. This hypothesis was not confirmed. The second hypothesis was that indices of force stabilizing synergies during fatigue would increase at both levels of the hierarchy. This hypothesis was partially confirmed only for group-index. The last hypothesis was that fatigue of TH would have stronger effects at the TH-VF level while fatigue of the index finger would have stronger effects at the IF level. This hypothesis was also partially confirmed.

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The superposition principle applied to grasping an object producing moments outside anatomically-defined axes

Cited by 4 publications

References 22 publications

Decoupled Control of Grasp and Rotation Constraints During Prehension of Weightless Objects

Decoupled Control of Grasp and Rotation Constraints During Prehension of Weightless Objects

Superposition of Automatic and Voluntary Aspects of Grip Force Control in Humans during Object Manipulation

Prehension Synergies During Fatigue of a Single Digit: Adaptations in Control With Referent Configurations

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