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

Abstract

In this experiment we examined the coupling between grip force and load force observed during cyclic vertical arm movements with a hand-held object, performed in different gravitational environments. Six subjects highly experienced in parabolic flight participated in this study. They had to continuously move a cylindrical object up and down in the different gravity fields (1g, 1.8 g and 0 g) induced by parabolic flights. The imposed movement frequency was 1 Hz, the object mass was either 200 or 400 g, the amplitude of movement was either 20 or 40 cm and an additional mass of 200 g could be wound around the forearm. Each subject performed the task during 15 consecutive parabolas. The coordination between the grip force normal to the surface and the tangential load force was examined in nine loading conditions. We observed that the same normal grip force was used for equivalent loads generated by changes of mass, gravity or acceleration despite the fact that these loads required different motor commands to move the arm. Moreover, our results suggest that the gravitational and inertial components of the load are treated adequately and independently by the internal models used to predictively control the required grip force. These results indicate that the forward internal models used to control precision grip take into account the dynamic characteristics of the upper limb, the object and the environment to predict the object's acceleration and, in turn, the load force acting at the fingertips.

Sensorimotor Mapping for Anticipatory Grip Force Modulation

“…Similar results were reported in the context of oscillatory movements by White et al (2005) who showed that the grip force was adjusted to the actual load despite the fact that the variation of load force resulted from a distinct combination of object mass, movement acceleration, and gravity. In the present context of discrete movements, independent prediction must be estimated for each trial, which presumably hardens a fine GF adjustment relative to the actual load.…”

Production of finely graded forces in humans: effects of simulated weightlessness by water immersion

“…Similarly, deWcits of force production were found to persist throughout the alternating episodes of high and low gravitational pull in parabolic Xight (Mierau et al 2008) and were only in part compensated by 10 min of continuous practice in a rotating centrifuge (Goebel et al 2006). Thus, taken together, the observed deWcits of force production seem to markedly conXict another line of research that found no deWcits in the coupling of grip and load forces during object manipulation in parabolic Xight (Hermsdörfer et al 1999;Hermsdörfer et al 2000;White et al 2005;Augurelle et al 2003), except for the very Wrst trials of unexperienced subjects (Augurelle et al 2003). However, the apparent conXict can easily be resolved.…”

Delayed Visual Feedback Affects Both Manual Tracking and Grip Force Control When Transporting a Handheld Object

“…Predictive mechanisms have been demonstrated in motor behaviors as diverse as object manipulation, locomotion, gaze orientation, or manual tracking (Bastian 2006;Flanagan et al 2003;Miall and Jackson 2006;Vaziri et al 2006). For instance, when we manipulate a handheld object, grip force is largely determined by predictive mechanisms, as evidenced by its modulation preceding or being in synchrony with the destabilizing load force resulting from the hand movement (i.e., tangential load at the object-finger interface; Danion and Sarlegna 2007;Davare et al 2007;Johansson and Westling 1988a;White et al 2005;Zatsiorsky et al 2005). Moreover, such anticipatory adjustments are observed irrespectively of the number of hands or fingers used to hold the object (de Freitas and Jaric 2009;Flanagan and Tresilian 1994).…”