Bimanual coordination between isometric contractions and rhythmic movements: an asymmetric coupling

Abstract

Interactions between rhythmically moving limbs typically result in attraction to a limited number of coordination modes, which are distinguished in terms of their stability. In addition, the stability of coordination typically decreases with elevations in movement frequency. To gain more insight into the neurophysiological mechanisms underlying these stability characteristics, the effects of phasic voluntary muscle activation onto the movement pattern of the contralateral limb as well as onto the stability of interlimb coordination were examined. This was done in circumstances in which a minimal degree of movement-elicited afferent information was available to mediate the coupling influences. The task involved rhythmic application of isometric torque by one hand, while the other hand was moving rhythmically with unconstrained amplitude. The effects of two levels of applied torque, two coordination patterns (inphase and antiphase), and two movement frequencies were determined, both at the behavioural level (movement kinematics and kinetics) and the neuromuscular level (EMG). The isometric applications of torque clearly influenced the muscle-activation profile and movement pattern of the other limb, affecting both temporal variability and amplitude. Surprisingly, there were no differences between the two coordination patterns or between the tempo conditions. As such, the results did not conform to the Haken-Kelso-Bunz model for rhythmic movement coordination. These data suggest that the archetypal differences in stability of rhythmic bimanual coordination are contingent upon a correspondence between the limbs in terms of their respective tasks. This interpretation is elaborated in terms of the role of sensory feedback and the functional specificity of motor unit recruitment in rhythmic interlimb coordination.

The effects of task demands on bimanual skill acquisition

“…Our unexpected finding may be due the fact that this is isometric task, as opposed to other bimanual tasks that have been studied such as reaching (Peper and Carson 1999). Our task may have had easier timing requirements.…”

“…For example, when individuals produce asymmetric bimanual reaching movements with different amplitudes, the hand that reaches the shorter distance may overshoot because it is temporally constrained with the hand that reaches farther (Heuer et al 1998; Marteniuk et al 1984). In comparison, force amplitude and timing have been demonstrated to be relatively independent (Peper and Carson 1999; Gordon and Ghez 1987) which may make it easier to produce asymmetric forces.…”

Relative phase dynamics in perturbed interlimb coordination: the effects of frequency and amplitude

“…If the researcher's objective is to gain deeper knowledge about a particular type of behavior, it remains a perfectly valid enterprise to search for the coupling function which speci®cally applies to the studied phenomenon. As pointed out, for instance, by Peper and Carson (1999), coordinative phenomena may be contingent upon sensory feedback and bilateral motor activation processes. In both the identi®ed scenarios, the question remains how coordination principles at the behavioral level correspond to the functional organization of the nervous system.…”

Bilateral motor unit synchronization is functionally organized

“…To examine the interactions and processes underlying bimanual coordination, bilateral coupling has been probed by manipulating various parameters, including movement tempo and amplitude (Peper et al 1995;Post et al 2000a, b), amount of torque applied (Peper and Carson 1999), handedness (TreVner and Turvey 1996), attention (Swinnen et al 1996;Amazeen et al 1997), and more. Remarkably, muscle fatigue has hardly been investigated in this context, even though it appears a particularly expedient vehicle to gain insight T. W. Boonstra (&) · A. DaVertshofer · E. van As · S. van der Vlugt · P. J. Beek Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9, 1081BT Amsterdam, The Netherlands e-mail: t.boonstra@fbw.vu.nl into the interactions governing interlimb coordination.…”