Force coordination in static manipulation tasks: effects of the change in direction and handedness

Abstract

A number of studies have demonstrated high coordination of the hand grip force (GF; normal component of force acting at the digits-object contact area) and load force (LF; tangential component) in a variety of manipulation tasks. The aim of the study was to explore the mainly neglected effect of the change in LF direction and the effect of handedness on GF and LF coordination in bimanual manipulation task. Subjects (N = 14) exerted a bimanual sinusoidal LF pattern against externally fixed handles in trials that gradually changed from unidirectional (LF exerted only in one direction) to fully bidirectional (equal LF peaks in two opposite directions). Despite the gradual change of LF, unidirectional trials demonstrated high indices of force coordination, while in all bidirectional trials, no matter how low and brief LF exertion was in the opposite direction, all indices of GF and LF coordination deteriorated to a considerably lower level. The non-dominant hand demonstrated both a higher directional accuracy of exerting LF and higher GF modulation than the dominant one. We concluded that manipulation tasks performed in a single and two alternating directions may be based on partly distinctive neural control mechanisms, as well as that a switching of muscle synergies required in bidirectional tasks could play a role in the observed phenomenon. Regarding the effect of hand dominance, the recorded advantage of the non-dominant hand could be considered as an addition to the current views of the non-dominant arm/hemisphere specialization in controlling limb position.

Paresthesias as Reflection of the Lateral Asymmetry of Neural Function in Human

“…The selective hemispheric activation may thus play a role in the motor output asymmetry in human extremities. Assuming that the afferent sensory feedback is the neural basis for interlimb coordination and contributes strongly to the modulation of the spinal reflexes as well as control on supraspinal levels (Freitas et al, 2007;Pearson and Gordon, 2000;Rothwell, 1996;Zehr et al, 2004;Zehr, 2006), it was hypothesized that the functional dominance in limbs may be an important modulating factor for the motor coordination (Olex-Zarychta & Raczek, 2008;Olex-Zarychta, 2010). Earlier studies indicated asymmetries in the number of corticospinal axons (Nathan et al, 1990) as well as in cortical representations of the dominant limb muscles (Nudo, 1992) and brought evidences supporting the adaptive plasticity in muscle and cutaneous afferent reflex pathways induced by training and rehabilitative interventions.…”

Force coordination in static manipulation: Discerning the contribution of muscle synergies and cutaneous afferents

“…In line with both our and other authors' studies, we assessed the coordination of G and L by calculating G/L ratio, the maximum cross correlation coefficient between G and L and their respective time lags, as well as the G modulation through G gain and offset [4,7,11,12,32]. Fig.…”

“…A number of daily activities involve bidirectional tasks, such as operating tools, shaking vigorously an object, or using external support under dynamical conditions. Only recently we compared the uni-and bidirectional static manipulation tasks [4,12] and observed an abrupt deterioration in G-L coordination whenever the subjects switched from uni-to bidirectional tasks. We interpreted the findings using the concept of muscle synergies.…”

“…Both sides of the handle were covered by rubber. The remaining two components acting tangentially (vertical F Z and horizontal F X ) were used to calculate the load force (L) that tended to cause slippage [4]. When F Z acted upward and downward, L was considered positive and negative, respectively.…”

“…To manipulate the extent to which F Z was exerted in one with respect to the opposite direction, we manipulated the index of bidirectionality (IB) by gradually lowering F Z min [4]. Specifically, we calculated the prescribed IB as:…”