Coupling of grip force and load force during arm movements with grasped objects

Werremeyer, Mary M. and Kelly J. Cole. Wrist action affects precision grip force. J. Neurophysiol. 78: 271–280, 1997. When moving objects with a precision grip, fingertip forces normal to the object surface (grip force) change in parallel with forces tangential to the object (load force). We investigated whether voluntary wrist actions can affect grip force independent of load force, because the extrinsic finger muscles cross the wrist. Grip force increased with wrist angular speed during wrist motion in the horizontal plane, and was much larger than the increased tangential load at the fingertips or the reaction forces from linear acceleration of the test object. During wrist flexion the index finger muscles in the hand and forearm increased myoelectric activity; during wrist extension this myoelectric activity increased little, or decreased for some subjects. The grip force maxima coincided with wrist acceleration maxima, and grip force remained elevated when subjects held the wrist in extreme flexion or extension. Likewise, during isometric wrist actions the grip force increased even though the fingertip loads remained constant. A grip force “pulse” developed that increased with wrist force rate, followed by a static grip force while the wrist force was sustained. Subjects could not suppress the grip force pulse when provided visual feedback of their grip force. We conclude that the extrinsic hand muscles can be recruited to assist the intended wrist action, yielding higher grip-load ratios than those employed with the wrist at rest. This added drive to hand muscles overcame any loss in muscle force while the extrinsic finger flexors shortened during wrist flexion motion. During wrist extension motion grip force increases apparently occurred from eccentric contraction of the extrinsic finger flexors. The coactivation of hand closing muscles with other wrist muscles also may result in part from a general motor facilitation, because grip force increased during isometric knee extension. However, these increases were related weakly to the knee force. The observed muscle coactivation, from all sources, may contribute to grasp stability. For example, when transporting grasped objects, upper limb accelerations simultaneously produce inertial torques at the wrist that must be resisted, and inertial loads at the fingertips from the object that must be offset by increased grip force. The muscle coactivation described here would cause similarly timed pulses in the wrist force and grip force. However, grip-load coupling from this mechanism would not contribute much to grasp stability when small wrist forces are required, such as for slow movements or when the object's total resistive load is small.

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Flexible organization of grip force control during movement frequency scaling

Journal of Neurophysiology ◽

10.1152/jn.00416.2019 ◽

2019 ◽

Vol 122 (6) ◽

pp. 2304-2315

Author(s):

Francis M. Grover ◽

Sarah M. Schwab ◽

Paula L. Silva ◽

Tamara Lorenz ◽

Michael A. Riley

Keyword(s):

Force Control ◽

Grip Force ◽

Sagittal Plane ◽

Oscillation Amplitude ◽

Load Force ◽

Force Load ◽

Grip Force Control ◽

Force Coupling ◽

Tightly Coupled ◽

Oscillation Frequencies

The grip force applied to maintain grasp of a handheld object has been typically reported as tightly coupled to the load force exerted by the object as it is actively manipulated, occurring proportionally and consistently in phase with changes in load force. However, continuous grip force-load force coupling breaks down when overall load force levels and oscillation amplitudes are lower (Grover F, Lamb M, Bonnette S, Silva PL, Lorenz T, Riley MA. Exp Brain Res 236: 2531–2544, 2018) or more predictable (Grover FM, Nalepka P, Silva PL, Lorenz T, Riley MA. Exp Brain Res 237: 687–703, 2019). Under these circumstances, grip force is instead only intermittently coupled to load force; continuous coupling is prompted only when load force levels or variations become sufficiently high or unpredictable. The current study investigated the nature of the transition between continuous and intermittent modes of grip force control by scaling the load force level and the oscillation amplitude continuously in time by means of scaling the required frequency of movement oscillations. Participants grasped a cylindrical object between the thumb and forefinger and oscillated their arm about the shoulder in the sagittal plane. Oscillation frequencies were paced with a metronome that scaled through an ascending or descending frequency progression. Due to greater accelerations, faster frequencies produced greater overall load force levels and more pronounced load oscillations. We observed smooth but nonlinear transitions between clear regimes of intermittent and continuous grip force-load force coordination, for both scaling directions, indicating that grip force control can flexibly reorganize as parameters affecting grasp (e.g., variations in load force) change over time. NEW & NOTEWORTHY Grip force (GF) is synchronously coupled to changing load forces (LF) during object manipulation when LF levels are high or unpredictable, but only intermittently coupled to LF during less challenging grasp conditions. This study characterized the nature of transitions between synchronous and intermittent GF-LF coupling, revealing a smooth but nonlinear change in intermittent GF modulation in response to continuous scaling of LF amplitude. Intermittent, “drift-and-act” control may provide an alternative framework for understanding GF-LF coupling.

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Importance of Cutaneous Feedback in Maintaining a Secure Grip During Manipulation of Hand-Held Objects

Journal of Neurophysiology ◽

10.1152/jn.00249.2002 ◽

2003 ◽

Vol 89 (2) ◽

pp. 665-671 ◽

Cited By ~ 181

Author(s):

Anne-Sophie Augurelle ◽

Allan M. Smith ◽

Thierry Lejeune ◽

Jean-Louis Thonnard

Keyword(s):

Internal Model ◽

Grip Force ◽

Tangential Force ◽

Safety Margin ◽

Background Level ◽

Load Force ◽

Initial Contact ◽

Phase Lag ◽

Cutaneous Sensation ◽

Hold Period

Previous research has shown that grip and load forces are modulated simultaneously during manipulation of a hand-held object. This close temporal coupling suggested that both forces are controlled by an internal model within the CNS that predicts the changes in tangential force on the fingers. The objective of the present study was to examine how the internal model would compensate for the loss of cutaneous sensation through local anesthesia of the index and thumb. Ten healthy adult subjects (5 men and 5 women aged 20–57 yr) were asked to grasp, lift, and hold stationary, a 250 g object for 20 s. Next, the subjects were asked to perform vertical oscillatory movements over a distance of 20 cm at a rate of 1.0 Hz for 30 s. Eleven trials were performed with intact sensation, and 11 trials after a local ring-block anesthesia of the index and thumb with bupivacain (5 mg/ml). During static holding, loss of cutaneous sensation produced a significant increase in the safety margin. However, the grip force declined significantly over the 20-s static hold period. During oscillatory arm movements, grip and load forces were continuously modulated together in a predictive manner as suggested by Flanagan and Wing. Again, the grip force declined over the 30-s movement, and 7/10 subjects dropped the object at least once. With intact sensation, the object was never dropped; but with the fingers anesthetized, it was dropped on 36% of the trials, and a significant slip occurred on a further 12%. The mean correlation between the grip and load forces for all subjects deteriorated from 0.71 with intact sensation to 0.48 after digital anesthesia. However, a cross-correlation calculated between the grip and load forces indicated that the phase lag was approximately zero both with and without digital anesthesia. Taken together, the data from the present study suggest that cutaneous afferents are required for setting and maintaining the background level of the grip force in addition to their phasic slip-detection function and their role in adapting the grip force/load force ratio to the friction on initial contact with an object. Finally, at a more theoretical level, they correct and maintain an internal model of the physical properties of hand-held objects.

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Do novel gravitational environments alter the grip-force/load-force coupling at the fingertips?

Experimental Brain Research ◽

10.1007/s00221-004-2175-8 ◽

2005 ◽

Vol 163 (3) ◽

pp. 324-334 ◽

Cited By ~ 32

Author(s):

Olivier White ◽

Joseph McIntyre ◽

Anne-Sophie Augurelle ◽

Jean-Louis Thonnard

Keyword(s):

Grip Force ◽

Load Force ◽

Force Load ◽

Force Coupling

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Force feedback delay affects perception of stiffness but not action, and the effect depends on the hand used but not on the handedness

Journal of Neurophysiology ◽

10.1152/jn.00822.2017 ◽

2018 ◽

Vol 120 (2) ◽

pp. 781-794 ◽

Cited By ~ 7

Author(s):

Raz Leib ◽

Inbar Rubin ◽

Ilana Nisky

Keyword(s):

Force Field ◽

Grip Force ◽

Force Feedback ◽

Internal Representation ◽

Elastic Force ◽

Perceptual Bias ◽

Load Force ◽

Test Case ◽

Robotic Device ◽

Left Handed

Interaction with an object often requires the estimation of its mechanical properties. We examined whether the hand that is used to interact with the object and their handedness affected people’s estimation of these properties using stiffness estimation as a test case. We recorded participants’ responses on a stiffness discrimination of a virtual elastic force field and the grip force applied on the robotic device during the interaction. In half of the trials, the robotic device delayed the participants’ force feedback. Consistent with previous studies, delayed force feedback biased the perceived stiffness of the force field. Interestingly, in both left-handed and right-handed participants, for the delayed force field, there was even less perceived stiffness when participants used their left hand than their right hand. This result supports the idea that haptic processing is affected by laterality in the brain, not by handedness. Consistent with previous studies, participants adjusted their applied grip force according to the correct size and timing of the load force regardless of the hand that was used, the handedness, or the delay. This suggests that in all of these conditions, participants were able to form an accurate internal representation of the anticipated trajectory of the load force (size and timing) and that this representation was used for accurate control of grip force independently of the perceptual bias. Thus these results provide additional evidence for the dissociation between action and perception in the processing of delayed information. NEW & NOTEWORTHY Introducing delay to force feedback during interaction with an elastic force field biases the perceived stiffness of the force field. We show that this bias depends on the hand that was used for probing but not on handedness. At the same time, both left-handed and right-handed participants adjusted their applied grip force while using either their left or right hands in anticipation of the correct magnitude and timing despite the delay in load force.

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Hand Interactions in Rapid Grip Force Adjustments Are Independent of Object Dynamics

Journal of Neurophysiology ◽

10.1152/jn.90593.2008 ◽

2008 ◽

Vol 100 (5) ◽

pp. 2738-2745 ◽

Cited By ~ 20

Author(s):

Olivier White ◽

Noreen Dowling ◽

R. Martyn Bracewell ◽

Jörn Diedrichsen

Keyword(s):

Grip Force ◽

Object Manipulation ◽

Load Force ◽

Single Object ◽

Stereo Display ◽

Force Increase ◽

Robotic Devices ◽

The Moment ◽

Pure Measurement ◽

Object Dynamics

Object manipulation requires rapid increase in grip force to prevent slippage when the load force of the object suddenly increases. Previous experiments have shown that grip force reactions interact between the hands when holding a single object. Here we test whether this interaction is modulated by the object dynamics experienced before the perturbation of the load force. We hypothesized that coupling of grip forces should be stronger when holding a single object than when holding separate objects. We measured the grip force reactions elicited by unpredictable load perturbations when participants were instructed to hold one single or two separate objects. We simulated these objects both visually and dynamically using a virtual environment consisting of two robotic devices and a calibrated stereo display. In contrast to previous studies, the load forces arising from a single object could be uncoupled at the moment of perturbation, allowing for a pure measurement of grip force coupling. Participants increased grip forces rapidly (onset ∼70 ms) in response to perturbations. Grip force increases were stronger when the load force on the other hand also increased. No such coupling was present in the reaction of the arms to the load force increase. Surprisingly, however, the grip force interaction did not depend on the nature of the manipulated object. These results show fast obligatory coupling of bimanual grip force responses. Although this coupling may play a functional role for providing stability in bimanual object manipulation, it seems to constitute a relatively hard-wired modulation of a reflex.

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Smart switching in feedforward control of grip force during manipulation of elastic objects

10.1101/194407 ◽

2017 ◽

Cited By ~ 2

Author(s):

Olivier White ◽

Amir Karniel ◽

Raz Leib ◽

Charalambos Papaxanthis ◽

Marie Barbiero ◽

...

Keyword(s):

Control Systems ◽

Grip Force ◽

Feedforward Control ◽

Load Force ◽

Switching Systems ◽

State Variables ◽

Discrete State ◽

Research Questions ◽

New Research ◽

The Brain

AbstractSwitching systems are common in artificial control systems. Here, we suggest that the brain adopts a switched feedforward control of grip forces during manipulation of objects. We measured how participants modulated grip force when interacting with soft and rigid virtual springs when stiffness varied nearly continuously between trials. We identified a sudden phase transition between two forms of feedforward control that differed in the timing of the synchronization between the anticipated load force and the applied grip force. The switch occurred several trials after a threshold stiffness level. These results suggest that in the control of grip force, the brain acts as a switching control system. This opens new research questions as to the nature of the discrete state variables that drive the switching.

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